Translation:He is my brother now.
And what was he before?
His sister, isn't it obvious? :)
His sisters' boyfriend
You mean 'his sister's boyfriend'?
Either way, it's a complicated family situation. Best to stay out of it, I think. ;-)
attempts to resist temptation to write joke about Mormonism
unless he was the boyfriend of many of all his sisters!
Imagine. A couple gets married. They bought had already got children. The four of them will live together. One kid is telling about his new "brother". I know this sounds so ideal, I've only seen it on movies.
Oh, that happens in the US. Look carefully at that sentence though. "bought had got?", "They each already had children." would be better.
He has perhaps just joined the fraternity?