You probablly know I have twin sons. I also have a niece who moved in with us following the deaths of her parents. She was 16 when she moved in; the boys were 14.
Before that point in time, my boys and their cousin really got along great. She was the "glamorous older woman" in their young lives, and she was charmed by these two funny, rambunctious identical twin boys. Before she moved in they knew each other and liked each other. They played well together.
However, it was a real adjustment on everyones' part for the boys to suddenly "gain a sister". It's one thing to see a cousin once or twice a week. It's a whole different thing to find her makeup and hair care products in your bathroom. (Finding her Tampax in the cabinet was a severe shock to one of my boys. His face was drained of color.)
Even starting with a positive past history, there were a lot of ups and downs for my boys suddenly living with a pseudo-sister. Her adjustment was, of course, immense. She had lost both parents and was, suddenly, no longer an only child living in a girl-girl household with just her mother.
I tell you this to remind you that sibling relationships can be complex even under the best circs. Your situation is far from the "best" of circs. As I said before, I strongly suggest you contact your brother, make sure he has your contact info, then just wait.