I don't know how you can claim to know so much about Ewish culture and not know the divisions of the priest were among Aaron's two remaining sons, after his elder two were burnt up for burning strange fire before the Lord i the wilderness. The three divisions you're quoting is the divisions of the sons of Levi, and they were divided in 4 groups.
[FONT='Calibri','sans-serif']A. The three sons of Levi: Gershon, Kohath, Merari [/FONT]
1. Gershonites: (descendants of Gershon/Gershon, first son of Levi)
a. The Gershonites camped on the west side of the tabernacle: The families of the Gershonites were to camp behind the tabernacle westward (Numbers 3:23)
b. Their duties: Moving tabernacle covers, curtains, screens & cords with ox carts: Num 4:24-26; 7:7-8
1. "Now the duties of the sons of Gershon in the tent of meeting involved the tabernacle and the tent, its covering, and the screen for the doorway of the tent of meeting, and the hangings of the court, and the screen for the doorway of the court which is around the tabernacle and the altar, and its cords, according to all the service concerning them." (Numbers 3:25-26)
2. ""This is the service of the families of the Gershonites, in serving and in carrying: they shall carry the curtains of the tabernacle and the tent of meeting with its covering and the covering of porpoise skin that is on top of it, and the screen for the doorway of the tent of meeting, and the hangings of the court, and the screen for the doorway of the gate of the court which is around the tabernacle and the altar, and their cords and all the equipment for their service; and all that is to be done, they shall perform." (Numbers 4:24-26)
c. The Gershonites got two carts:
1. "
Two carts and four oxen he gave to the sons of Gershon, according to their service, and four carts and eight oxen he gave to the sons of Merari, according to their service, under the direction of Ithamar the son of Aaron the priest. But he did not give any to the sons of Kohath because theirs was the service of the holy objects, which they carried on the shoulder." (Numbers 7:7-9)
d. The 13 Levitical cities of the Gershonites:
1. Located within Issachar, Asher, Naphtali, Manasseh in Bashan
2. "The sons of Gershon received thirteen cities by lot from the families of the tribe of Issachar and from the tribe of Asher and from the tribe of Naphtali and from the half-tribe of Manasseh in Bashan." (Joshua 21:6)
2. Kohathites: (descendants of Kohath, second son of Levi, Aaron and Moses were Kohathites but had special rank)
a. The Kohathites camped on the south side of the tabernacle: Numbers 3:29
b. Duties: holy items like carrying the Ark of the Covenant, the lampstand, altars, utensils with poles:
1. "The families of the sons of Kohath were to
camp on the southward side of the tabernacle, and the leader of the fathers' households of the Kohathite families was Elizaphan the son of Uzziel. Now their duties involved the ark, the table, the lampstand, the altars, and the utensils of the sanctuary with which they minister, and the screen, and all the service concerning them; and Eleazar the son of Aaron the priest was the chief of the leaders of Levi, and had the oversight of those who perform the duties of the sanctuary." (Numbers 3:29-32)
2. Although the Kohathites were entrusted specifically with moving the Ark, David used the priests from Gershon, Merarites and Merari to move the Ark from the house of Obed-edom after Uzzah died in the first attempt: (1 Chronicles 15:1-15)
a. "Now David built houses for himself in the city of David; and he prepared a place for the ark of God and pitched a tent for it. Then David said, "No one is to carry the ark of God but the Levites; for the LORD chose them to carry the ark of God and to minister to Him forever." And David assembled all Israel at Jerusalem to bring up the ark of the LORD to its place which he had prepared for it. David gathered together the sons of Aaron and the Levites: of the sons of Kohath,
Uriel the chief, and 120 of his relatives; of the sons of Merari,
Asaiah the chief, and 220 of his relatives; of the sons of Gershon, Joel the chief, and 130 of his relatives; of the sons of Elizaphan, Shemaiah the chief, and 200 of his relatives; of the sons of Hebron, Eliel the chief, and 80 of his relatives; of the sons of Uzziel, Amminadab the chief, and 112 of his relatives.
Then David called for Zadok and Abiathar the priests, and for the Levites, for Uriel, Asaiah, Joel, Shemaiah, Eliel and Amminadab, and said to them, "You are the heads of the fathers' households of the Levites; consecrate yourselves both you and your relatives, that you may bring up the ark of the LORD God of Israel to the place that I have prepared for it. "Because you did not carry it at the first, the LORD our God made an outburst on us, for we did not seek Him according to the ordinance." So the priests and the Levites consecrated themselves to bring up the ark of the LORD God of Israel. The sons of the Levites carried the ark of God on their shoulders with the poles thereon, as Moses had commanded according to the word of the LORD." (1 Chronicles 15:1-15)
c. The Kohathites got no carts but had to carry all the holy objects of furniture on poles and carrying bars:
1. The Kohathites did not get any carts like the Gershonites and the Merarites because they were exclusively entrusted with these holy items.
2. "Two carts and four oxen he gave to the sons of Gershon, according to their service, and four carts and eight oxen he gave to the sons of Merari, according to their service, under the direction of Ithamar the son of Aaron the priest.
But he did not give any to the sons of Kohath because theirs was the service of the holy objects, which they carried on the shoulder." (Numbers 7:7-9)
3. "This is the work of the
descendants of Kohath in the tent of meeting, concerning the most holy things. When the camp sets out, Aaron and his sons shall go in and they shall take down the veil of the screen and cover the ark of the testimony with it; and they shall
lay a covering of porpoise skin on it, and shall spread over it a cloth of pure blue, and shall
insert its poles. Over the table of the bread of the Presence they shall also
spread a cloth of blue and put on it the dishes and the pans and the sacrificial bowls and the jars for the drink offering, and the continual bread shall be on it. They shall spread over them a cloth of scarlet material, and cover the same with a covering of porpoise skin, and they shall
insert its poles. Then they shall take a
blue cloth and cover the lampstand for the light, along with its lamps and its snuffers, and its trays and all its oil vessels, by which they serve it; and they shall put it and all its utensils in a covering of porpoise skin, and shall
put it on the carrying bars. Over the golden altar they shall spread a blue cloth and
cover it with a covering of porpoise skin, and shall insert its poles; and they shall take all the utensils of service, with which they serve in the sanctuary, and put them in a blue cloth and cover them with a covering of porpoise skin, and put them on the
carrying bars. (Numbers 4:412)
d. The 23 Levitical cities of the Kohathites:
1. Located in Ephraim, Dan, Manasseh in Canaan
2. "Then the lot came out for the families of the Kohathites. And the sons of Aaron the priest, who were of the Levites, received thirteen cities by lot from the tribe of Judah and from the tribe of the Simeonites and from the tribe of Benjamin. The rest of the sons of Kohath received ten cities by lot from the families of the tribe of Ephraim and from the tribe of Dan and from the half-tribe of Manasseh." (Joshua 21:4-5)
3. Merarites: (descendants of Merari, third son of Levi)
a. Merarites camped on the north side of the tabernacle: Numbers 3:33-37
b. Their duties: Moving tabernacle poles, boards, sockets, pillars and bars by hand. Each item is assigned individually to a man who carries it with his bare hands: Num 3:36-37; 4:29-33
1. "The Levites, however, were not numbered among them by their fathers' tribe. For the LORD had spoken to Moses, saying, "Only the tribe of Levi you shall not number, nor shall you take their census among the sons of Israel. "But you shall appoint the Levites over the tabernacle of the testimony, and over all its furnishings and over all that belongs to it. They shall carry the tabernacle and all its furnishings, and they shall take care of it; they shall also camp around the tabernacle. "So when the tabernacle is to set out, the Levites shall take it down; and when the tabernacle encamps, the Levites shall set it up. But the layman who comes near shall be put to death. "The sons of Israel shall camp, each man by his own camp, and each man by his own standard, according to their armies. "But the Levites shall camp around the tabernacle of the testimony, so that there will be no wrath on the congregation of the sons of Israel. So the Levites shall keep charge of the tabernacle of the testimony."" (Numbers 1:47-53)
2. "Of Merari was the family of the Mahlites and the family of the Mushites; these were the families of Merari. Their numbered men in the numbering of every male from a month old and upward, were 6,200. The leader of the fathers' households of the families of Merari was Zuriel the son of Abihail.
They were to camp on the northward side of the tabernacle. Now the appointed duties of the sons of Merari involved the frames of the tabernacle, its bars, its pillars, its sockets, all its equipment, and the service concerning them, and the pillars around the court with their sockets and their pegs and their cords." (Numbers 3:33-37)
3. "As for the sons of Merari, you shall number them by their families, by their fathers' households; from thirty years and upward even to fifty years old, you shall number them, everyone who enters the service to do the work of the tent of meeting. "Now this is the duty of their loads, for all their service in the tent of meeting: the boards of the tabernacle and its bars and its pillars and its sockets, and the pillars around the court and their sockets and their pegs and their cords, with all their equipment and with all their service;
and you shall assign each man by name the items he is to carry. "This is the service of the families of the sons of Merari, according to all their service in the tent of meeting, under the direction of Ithamar the son of Aaron the priest." (Numbers 4:29-33)
There were 3 divisions and they all had specific duties.