One tenant threatened another with violence - what should I do?

[Jim Young]

I rent a townhouse to three adult college students on three individual leases co-signed by their parents. I got a call from tenant A's father who said that tenant B threatened tenant C.  He went on to say that tenant B was suffering from mental health issues exacerbated by the COVID shutdowns.  Tenant's A and C feel unsafe and have moved out of the unit into tenant A's father's house.

I asked to speak with tenant A and C to hear their side.  It sounds like it was a verbal threat.  They do not want to involve the police.  There is language in the lease that could probably be used for an eviction case but it's not black and white.  I said I wanted to speak to tenant B first but I am open to the idea of finding a suitable replacement roommates to assume the leases, as long as the roommates meet my original screening criteria.

I spoke to tenant B and made the same offer, and tenant B was open to it.  I encouraged them to work it out between themselves and let me know what they want to do.  I offered to market the unit on Zillow etc. if they want to look for another roommate.

That's where it stands.  Tenant A's father (a co-signer) would like to see it resolved. 

What red flags do you see?  I'm thinking I should put an ad out for new roommates and ask tenants A, B and C who wants to move out. I'd probably let A and C break the lease and give B cash for keys if it came to it.  I'd love to hear some other ideas.  Thanks!