Rent by Room- Inappropriate Tennant Behavior

[Travis Rush]

Hello all, I'm a new investor renting my first property out by the room and I need some advice on a difficult situation. There are three tenants in the single family home.

I recently received troubling reports form Roommate A (female) that Roommate B (male) has been acting inappropriately. Most of these events were also witnessed by Roommate C. Apparently Roommate B has been cornering Roommate A in the common spaces and standing uncomfortably close. It escalated to one event where Roommate B grabbed Roommate A's arm. This is completely inappropriate and I have asked that Roommates A and C please write me an email containing all inappropriate behavior by Roommate B. I have had small, unrelated issues with Roommate B in the past (small things like loud music and failure to clean up after himself in the kitchen).

My issue is that I clearly don't want any of this behavior going on inside my property, but I don't have anything in the lease that expressly states personal boundaries and I'm not sure that this would constitute a violation of law. It seem that they have discussed the issue with Roommate B, but he has been obstinate. 

Is a notice to vacate appropriate here? How long would the notice need to be? If a written warning is necessary first, I'm not sure exactly how to phrase it. Any guidance would be much appreciated. I will be adding things like this to my future leases.

Thank you.