You did not answer the question. It was fairly asked. It is a simple question about Greek.
What Greek word would I use if I were to talk of your brother?
So far as children of Mary is concerned, there are passages that suggest Mary accompanied Jesus' brothers and sisters.
We can deal with that in a few ways:
1. They are Mary's children.
2. They are Joseph's children by a different marriage either before or after his marriage to Mary.
3. They "possibly" could be cousins based on that minor usage of "brother" to mean kinfolk.
I've been honest with you. Your turn.
Just because one would use the word 'adelphoi' to talk of siblings (from the same parents) does not mean that 'adelphoi' can only mean 'siblings from the same parents', especially since there are different senses of the term, as St. Jerome points out, not just as used in Greek, but also and especially as used in Aramaic.
-A8