Do you think they're still true friends knowing that they involved your parents? Wake up dude! I also have bully friends but they never involved my family in such things because its too personal.
I don't really even know it right now, I kept on thinking what should I do now. Another thing is they are my group mates on thesis.
Talk to them personally and tell them what you really feels inside. It's hard to work on a group project if you have discomfort or hard feelings to other members. Conflicts may exist in your decision making regarding to your thesis because the decision is not unanimous. In order to prevent that from happening, you should open up with them, tell them everything, ask them what they want and what they really after. If they stop it then its okay, but if they ignore everything you say then its time for you to decide whether to stick with them or ask your professor to let you join other group. Good luck bro!