I understand you are referring to the Greek. I am not a Greek scholar
That is something we have in common then, because neither am I. Fortunately, we don’t have to be. Faithful Greek lexicons and concordances are at our fingertips, which demonstrates “sister” in Greek only has two meanings, and a non-uterine familial relationship is not one of them:
Sister (adelphe) - Strong’s Concordance
There is no word for biological brother in either Aramaic, which Jesus spoke, or in Hebrew.
Not a word strictly assigned to it, you are correct, but it can and does use the same word to describe a uterine relationship. But the NT was written in Greek, not Hebrew or Aramaic, which is more specific, particularly with “sister” (adelphe), as you can see for yourself from the link to the concordance, which has only TWO meanings, unlike adelphoi for “brother.”
And then in regards to brothers, even the people who saw Jesus after His resurrection were referred to as brothers, all 500 of them but Mary did not give birth to 500 sons.
LOL! Protestants have never claimed that “brothers” in Greek can ONLY mean uterine! Of course it has multiple meanings! So if that is your argument, then to be consistent, does that mean James and John were not biological “brothers” then, since the NT uses the same Greek word to describe their relationship? Protestants don’t use only “one” meaning of a Greek word to define all other uses of its use in Scripture. They discern its meaning based on its context, by comparing its use in a verse by not only its Greek meaning, but also cross-referencing other related passages in Scripture as well.
So from the earliest days of Christianity, the Church has believed that Mary was a perpetual virgin, and Jesus had no biological brothers or sisters.
It is true that most ECFs espoused to this dogma. But it also acknowledges that not “all” of them did, particularly the closer you get to the first couple centuries. This inconsistency with a truly “universal” agreement is why Protestants look to Scripture, and exegete the context and cross-reference related passages, utilizing the original Biblical languages to attempt to discern the context of particular passages, including one’s not everyone in antiquity agreed on.
Again, this is from the Protestant perspective and NOT meant to challenge anything.