I would think you should build up a bit of paperwork in case you need to defend your self in front of a judge. maybe something in writing from past tenant. maybe a couple calls to police for noise complaints. have you talked to tenant about the issue?

If you say something to him, both of them will gang up on you and she’ll defend him.

Sounds like an excuse to defend buying low class and low quality rentals then blaming the government for you buying a high risk asset.

If they don't name all individuals in the beginning of the lawsuit and sufficient time passes, they cannot later add defendants to the suit.