My response:
Okay, I see that you edited your original post to show California (my State of Practice).
Since California is not a Common Law marriage State, Mom and Boyfriend are not married. Since that is the case, all Mom has to do is follow the Landlord / Tenant laws of California, starting with having him served with a 30 day Notice to Vacate.
If he's abusive, or if Mom is scared that he will become abusive if she follows through with the above, then if she has the proper "grounds", she can immediately, and on her own, go to the Criminal Courts building and file for a Temporary Restraining Order. Then have him served with a 30 day Notice to Vacate.
If you run a search of this Board, by using "Restraining", because we have covered this subject many, many times, and you'll get all the instructions for doing so. Just read all of the posts.
Your Mom will need an attorney for the Eviction Process, however.
Good luck.
IAAL