I'm going to get my girlfriend and her mom in trouble at work
Why would you get them in trouble?
I really want to get rid of them both.
It's not nice to cause people issues at their work. You should leave them alone.
I'm going to tell them that my girlfriend is a thief and her mom lied about her degree.
That is not going to be a good thing to do at their workplace. I highly recommend you find a private setting to express the problems you have with them. This will be beneficial to both parties.