Firstborn does not mean onlyborn.
For the ancient Jews firstborn meant the child that opened the womb (Ex. 13:2; Num. 3:12). Under the Mosaic Law, it was the "first-born" son that was to be sanctified (Ex. 34:20). Did this mean the parents had to wait until a second son was born before they could call their first the "first-born"? Hardly. The first male child of a marriage was termed the "first-born" even if he turned out to be the only child of the marriage.
Moreover to be the ‘first-born’ was a very important title in that culture, since among other things, it implied the person would receive two thirds of the inheritance. It does not refer only to the fact of being the first one to be born, since the older son, even if the only one would be called ‘first-born’. Heb 1:6 is a reference to God sending his first-born Son into the world. Who would be others sent by God with the same dignity as Jesus?
‘First-born’ refers to a privilege, without having to have had other sons or children. If the ‘first-born’ were at the same time the ‘only-born’, the first title would count for more.
The word until (or till) denotes a point in time up to which some action occurred. It does not mean that the action changed, only that there was something significant about that point in time. That point in time may be significant for reason other than a change in the action. What happened after that may be explicitly stated or may be inferred from the context, or may just be left unknown. To claim it always means the action changes is not valid and leads to absurdities.
Mt 1:25 cannot be used to prove that Mary had a sexual relationship with Joseph. To infer it is to claim what has yet to be proved.
Consider this line: "Michal the daughter of Saul had no children till the day of her death" (2 Sam. 6:23).
Are we to assume therefore she had children after her death?
“There was also a prophetess, Anna, the daughter of Phanuel, of the tribe of Asher. She was advanced in years, having lived seven years with her husband after her marriage, and then as a widow until she was eighty-four.” Lk 2:36-37).
Does that imply she got married at the age of 84?
Until I arrive, attend to the reading, exhortation, and teaching.(1Tim 4:13)
After Paul arrives will Timothy stop reading, exhortation and teaching?
The first point is that there are different kinds of brothers (and sisters) - full blood brothers, half brothers, adoptive brothers. If a man and woman marry and both have children by a previous marriage they will be regarded as brothers and sisters even though they have no genetic relationship. The actual relationship of these “brothers” to Jesus cannot be established unless a genealogy is given, and it is not.
Secondly the word brother can be used in a very loose sense. In Aramaic there is no word for cousin and the word for brother (aha) would include cousin or even nephew. Whilst Greek does include a word for cousin but it is quite possible to translators/writers just used the Greek adelphos to replace the Aramaic aha. Moreover the Greek word for brother (adelphos) was also used very loosely for various degrees of kinship.
In the Greek translation of the Old Testament (the LXX) the word adelphos is used for Lot’s nephew (Gen 14:14). Other similar examples can be given.
Paul says in Col 4:7 & 9
“Tychicus, my beloved brother (adelphos)……..together with Onesimus, a trustworthy and beloved brother (adelphos)”. We know from the letter to Philemon that Onesimus was actually a runaway slave, not Paul’s brother (or cousin).
Thirdly there indications in scripture that the brothers and sisters referred to in Mt 13:55 (and the equivalent in other gospels) are not Jesus brothers in any genetic sense.
I care very much about what scripture actually says.
It is you who are inventing what scripture does not say.
