Yay! I was quoted! Twice!
All in all, get over it. I'm sorry, but that's really all you can do.
I'm not that bad with kids, all my cousins are around 7 and below, and I get along great with them, but I wouldn't have been able to and probably won't be able to put up with them non-stop. I found out I was going to be a half-brother just before my Semester 1 exams, which was exactly what I need...Not. But I got over it. I didn't know whether I would hate my mother, the father, or the baby itself. But I couldn't do any of those, because doing any of those wouldn't help.
It was a tough time for my mother as well. I said that I didn't want to be a brother, and she understood that, and accepted that. But she needed my support.
That's why I decided, no matter what happens. I'm there to support my mum through this, above all else. And I still do, even after he's been born.
Ignoring the fact that they can be noisy or inconvenient at times, you don't have that much to worry about. Find yourself a good video game or some long-term thing you can do to stay away from the kids if you hate them that much.
Not in an attempt to avoid brotherly obligations and the like, I also happen to have 55 Gb of anime and a DS card that can hold up to 40 or so games.