A great coach helps pull out of your what your next best steps are, how to overcome the barriers in your way (logistical or even mental) and get more momentum. 

It's not his mental illness that is a problem.

If he is truly deranged or mentally unstable (possible with neat/bacteria-free issues)....you may be able to send a contractor (or multiple contractors) over to the crawlspace and leave some unpleasant smells, take pictures, and look for indications of illegal drugs.

t out of Luck if they don't have a letter of prescription from a correctly licensed mental health profession with a right to practice in the state that the individual lives. 

For the mentally ill, If they are really lucky, they have good family support.

What's amazing to me, is the amount of BS you have to deal with, when your properties are cheap, so many fake pay stubs, sketchy people, it's just different--  Different culture, different mentality, I'll just warn you, it won't be smooth sailing.     

Although instead of cancer, one of the tenants had a debilitating mental break. 

Put your mental energies to something else.

If I had ANY doubt as to his mental condition, I would contact lawyer/police.

@Joaquin CamarasaI'm going to pass on this as many of my "crazy tenant" experiences clearly involve underlying mental illness.