Quote from @Marshall Rousseau: They sound like awful tenants.When you expect something from someone, give them a deadline and a consequence for failing to respond."

For most people DIY is NOT a good option and will probably fail at anything you are trying to accomplish.This is not legal advice, it's practical advice.

A lift station failed during the last hurricane. 

Obviously, if the tenants fail to timely pay rent, you can enforce their obligations with a notice to pay.Your question is legal in nature, so I recommend that you consult your landlord or FHA attorney in your state about it.

My PM failed to let me know about the 21 day itemized rule, let alone initiate conversation with the the tenants for repairs and those tenants are refusing to pay anything past $4100 due to that technicality.  

I have seen several management companies in this area try to be "cheap" and they fail. 

The main reason businesses fail is because they run out of cash hence having a strong cash position as a business owner is vital. 

It depends on the terms and conditions of your application (hopefully you presented a formal offer to lease that provided for forfeiture of deposit if the tenant failed to take possession).

and these may be dumb questions but I don't mind looking stupid while I'm learning, I always fail up!! 

Sometimes parts fail and they get replaced and life goes on.