There are no biblical scriptures that says Mary stayed a virgin her whole life. The bible tells us that Joseph did not know his wife "till" she brought forth her firstborn son, and the meaning is clear that they "knew" each other afterward. So if you are reading the context that word "til" makes it known that Joseph did not have sex with Mary until she gave birth to Jesus.
Again, the insistence on a reversal of condition following the period of time covered by the preposition "until" is grammatically incorrect.
Further:
"The Lord said to my Lord, "Sit on my right until (ews an) I place your enemies under your feet." Matt. 22:44
Will He be no longer at the right ?
"Behold, I am with you always until (ews tin) the end of the age." Matt 28:20
Will Christ no longer be with us after the end of time ?
"And Michal daughter of Saul had no children until (ews tis) the day of her death." 2 Samuel 6:23
Did she bear children after her death ?
Scripture also says that Jesus had brothers and sisters, and therefore I am going to trust the eyewitnesses that are given an account.
The eyewitness did not provide any information on the precise relationship of the adelphos/adelphis; where a particular (among the many meanings) meaning is meant for this broad term, an additional description is given. There is none given in this case.
As the term "adelphos" can mean uncle/nephew (as used in the Bible), one could say with authority that these adelphos were uncles, for example. And, as Mary had a sister (adelphi) named Mary (according to the Gospel of John) one cannot read the word adelphos with "English meaning".
If you have proof that Mary stayed a virgin for life or that those "brothers and sisters" of Christ were not His siblings, I will gladly read the biblical verses, yes I mean biblical verses.
No Biblical proof has been provided that the adelphos were children born of Mary. No explanation has been provided for Mary's response to the announcement. No response has been given on the Biblical pattern of the younger son being the one preferred by God.
It cannot be Biblically shown that Mary and Joseph had any children.
But if your whole entire point is to tell us that Mary was a virgin for life and that Jesus' brothers and sisters were His "cousins" because that is what you were taught, then please don't bother, because if there is going to be a contradiction (even though you might not claim it to be a contradiction), I'll side with the word of God always.
Please provide conclusive Biblical evidence that the "adelphos" of Jesus were the children of Mary and Joseph.
Please provide an explanation for what the Holy Scripture records the betrothed Mary responds to the announcement of a future conception.
If the literal words of Holy Scripture are the final record for determining this matter, then it cannot be said with certainty that Mary had more than one Child, Jesus Christ.