BINGO!!! The one sentence that blows it out of the park.
I haven’t had time to read through many of the replies on this thread, so I don’t know if anyone else has replied on this, but that passage doesn’t support what you say. Unless Jesus’ brothers, if He had them, were believers, which they weren’t then, then there would be no way Jesus would leave His mother with them. The family of the Kingdom of Heaven was what Jesus was establishing, and unbelievers weren’t a part of it then. It would have been like Jesus leaving His Christian mother in the hands of Muslims. Second, even if these brothers were just cousins, one would think that if it was the blood tie that mattered here, they would still be under obligation to help their aunt who had no son. Clearly, though, again, it was the family of God that Jesus was going by, not the family of blood ties.