Yet most times a name is given, the mother turns out someone other than Mary. That is because the word "brother" and "sister" is used expansively, either as spiritual brothers or as kinsfolk. Jesus called "firstborn."
As a legal term. He is fuirstborn, regardless of siblings.
the force of a conjunction
whatever the grammatical category, it does not speak to the issue of marital relations after Christ was born.
Your reading of the Scripture is possible. It is however, not the only one possible, and yours happens to be heretical. Deal with it.
What a nice Christian attitude you have there.
Good day to you too annalex.
btt