This may be true. But this…
People don’t consider “fist cousins” to be a relationship that requires a separate category. The relationship is considered ambiguous such that if you feel a special bond with a cousin then you refer to him as “brother” (or “sister” if the cousin is female). Conversely, a “cousin” can be as distant as anyone else in society such that marrying your “fist cousin” is accepted and quite common.
Is just weird. I’m very close to a first cousin, and she and I never called each other “bro” or “sis.” We call each other “cuz.” I’ve never known anyone to do such a thing.
I also don’t think marrying a “first cousin” is either accepted or common, except among people (such as royalty) for whom “keeping it in the family” is important.
In other languages, this distinction exists; e.g. Chinese, not only is there a word for cousin, but separate words for cousins on the maternal and paternal side and phrases for older and younger and male and female cousins.
Jesus would have referred to his cousins as “brothers and sisters” in a direct translation from Aramaic to English. This in no way implies that Jesus had actual brothers and sisters.
I wish I had a link to this information, but it was told to me by my grandmother who was born and raised in Lebanon. She spoke Arabic, and she was from an area where a sprinkling of Aramaic was still present in their local dialect.
I’ll grant you that this is possible. But it also doesn’t address what is more likely; that Mary was a complete virgin for her entire life, or that she had a normal married, monogamous relationship with Joseph. The thing that grabs my interest is the need from men for Mary to be a lifelong virgin. Men do seem to put women into one of two buckets: Whore, or Virgin-saint. They put girls who enjoy sex into the former; they want to entertain the illusion that their mothers, wives and daughters are in the latter bucket.
Also, I stumbled upon this article which points out that the passage in question was written in Greek; if they were meant to be cousins, it could have used the Greek word for that (noting that even OT passages that were written in Hebrew are careful to distinguish brothers from cousins, even though there was no specific Hebrew word for it). It addresses certain other arguments as well. (The fact that the writer is female is merely a coincidence, and not a tie-in to the prior paragraph.)
Edit: On further review, the above link author’s scholarship is of dubious quality.