There's nothing you can do about it. Unfortunately, you have to grow up and deal. It's your mother's decision on whether or not she wants more kids. You can talk to her about your disatisfaction, and I'm sure that she'll probably keep the babies away from you.
If you don't like children, then you should stay away from them, hence why you need to tell your mother that you don't want to be near them. It might be a harsh pill for her to swallow, but the last thing those babies need is someone resenting them right out of the womb.
Granted, I don't really like children, either, but I don't really see what your true problem is.
If the crying gets to you, wear earbuds with your music up. If you don't want to change diapers, tell your parents that you won't. They can't force you to babysit, really, although they can definitely guilt trip you (God, I've had that done with me- and it was for my niece!). Personally, you'll find that you'll eventually come to love those children.
Don't you love your younger siblings, even if they can be... well, young?
Truthfully, there's nothing like seeing a baby smile for the first time. Then again, that may just be the female in me talking.