(CLV) Jn 18:28
They are, then, leading Jesus from Caiaphas into the pretorium. Now it was morning, and they did not enter into the pretorium lest they may be defiled, but may be (future tense) eating the passover.
Lev 15:10 And whoever touches anything that was under him shall be unclean until the evening. And whoever carries such things shall wash his clothes and bathe himself in water and be unclean until the evening.
Numbers 19: 22 Furthermore, anything the unclean person touches shall be unclean, and anyone who touches it shall be ceremonially unclean until evening.’”
These Scripture cannot refer to the Pesach Seder meal of the previous night and does not refer to the Unleavened bread eaten that evening, because in both cases, they would only be unclean until the evening and therefore points to something held during the day during the week of unleavened bread.
(CLV) Jn 19:14
Now it was the preparation of the Passover; the hour was about the third. And he is saying to the Jews, "Lo! your king!"
This is not the Passover Seder and it was the sixth hour not the third, check the translation.
While the Passover, strictly, is only one 24-hour period within the Feast of Unleavened Bread (which lasts for seven days), the name Passover can be applied to the whole seven days.
Luke 22:1 Now the Feast of Unleavened Bread drew near, which is called the Passover.
During the Feast of Unleavened Bread, they presented food offerings to the Lord for seven days, requiring them to remain ritually clean.
Lev 23:8 But you shall present a food offering to the Lord for seven days. On the seventh day is a holy convocation; you shall not do any ordinary work.”
(CLV) Jn 19:15
Yet they clamor then, "Away! Away! Crucify him!" Pilate is saying to them, "Shall I crucify your king?" The chief priests answered, "No king have we except Caesar!"
This occurring after the 15th during the Feast of Unleavened bread.