I will be purchasing property in CA, my Fiancé and I will be living at the property. His daughter will more than likely be living in one of the bedrooms. My question is, should I have her sign a rental agreement for my safety because I have been informed that she plans to move someone in (her violent tempered boyfriend) once they are out of jail. I am just worried I won't have the authority to remove him from my property. Thanks for any help.

Yes, you should have her sign a rental agreement that states that she cannot have anyone living with her or have overnight guests without your approval.

If she refuses to sign, then tell her to find her own place.

If you find that the boyfriend has stayed overnight, you can give her a 3 day notice for breach of the lease.