The first thing is handling any safty problems with the property. I would get a list from your tenants of all the safty problems in the property with pictures of you can and hire a local handy man to come and fix them all, and send you pictures of the completed projects.
After all the safety problem are fixed you start to have some choices. First choice is offer cash for keys and hope they take it. If they don't they might hold out until you can get an eviction. The good news is if they take it the sooner you can get your property back up and running!
Second option is hold out and collect as much rent as possible till you can evict them. Ethier way these tenants have to go If you want to ran a strong business.
Lessons to learn from this
First, don't accept partial rent. As soon as you accept money from a tenant it count as rent in the courts eyes no matter the amount you actually received
Second is make sure you have something in you lease that says no alteration can be made to the property with out owners consent.
Third is include your PM on any calls and emails you have with the tenants. By the sounds of it your PM quit because you have the option to reimburse the floor even though the PM said it was a bad idea.