My daughter (age 21) lives in our basement rent free. We have no lease or other document because she is our daughter. About a year back her boyfriend (age 25) moved in with her. She now realizes that the relationship is bad for her and wants to breakup with him and have him move out. Even his parents agree that she should dump him. She tried to breakup once before and he became threatening and violent. We want to plan for contingencies.

You have to evict him according to the laws where you live. If he becomes violent you call the police. You may then be able to get a restraining order to keep him away.