She said there wasn't much stuff whic I agreed because I visited him a couple of months ago to do a routine check up on the condo and found out he had no furniture and sleeping on a air mattress.  

We routinely offer to change out toilets to chair height (also known as ADA height).

As you stated the father routinely lets payments slip.

I discovered it when I went over there for routine maintenance, and told them that it was:A) Against their lease to modify the property without my written consent.B) Illegal to put a bedroom in the basement (insufficient methods of egress).C) A bad idea, because the basement gets damp with heavy rains.D) Improperly wired.I read them the part in the lease that they had verbally agreed to and signed, told them not to try that again, and they agreed to undo their electric work and remove the furniture from the basement. 

It's in good shape I will just need to do routine cleaning of the carpet. 

Do you have a clause in the lease that allows you to inspect the unit or perform routine maintenance with 24 hours notice?  

If there is evidence the child are being routinely being left unsupervised and are too young for that in your state, if you hear the parent hitting the children, if the children are not being fed (e.g. kids picking up food from other sources like the trash) these are reasons to call. 

If I felt I would routinely face such dangers I would get out of the landlording business.I respect others views on this board but I encourage you to think of the least savory, most unhinged tenant you have had, and then put a gun in their hands.

Above all else do not ever waver from your routine for anyone. 

Many types of fees (i.e. application fee, late fee, dishonored check fee, etc) can be, and are routinely, collected by most landlords.