Is this considered verbal abuse to the kids?

Parents should never EVER swear at their kids or tell them they're a mistake or anything of the sort. Parents can be annoying, yes, but insulting or cursing at children is wrong, always. If you're really concerned about your friends, go to your guidance councilor at school or your principal, whoever you can talk to, and tell them your concerns. They'll look into it, and if your friend -is- being abused, it will be taken care of.