If you fail to make your monthly house payments to the bank on time, that reflects on the Seller’s credit.

You're the one that will be paying the taxes, penalties, and consequences if you take this route and it fails.

I would give them suggested vendors, a consequence for failing to complete, a deadline to complete the work, and notice that I will inspect to verify the work is done to my satisfaction.After notifying the tenant, then I would contact the owner (phone or email, depending on their personal preference and my time) and let them know what happened and how I'm addressing it. 

The only thing you should be aware of is there is a section 8 specific inspection prior to move in that usually takes 1 month to complete so best case scenario is usually a section 8 tenant moves in in 2 months often its closer to 3 months if you fail the inspection and have to be reinspected which is common.

If you have a nuisance tenant (ex. tenant who pays rent but late every month, tenant who complains about things like "I saw A wasp or I'm getting the wrong mail in my mailbox,"  but fails to report legitimate issues in a timely manner, tenant who fails to get along with the neighbors), you won't be able to get that nuisance tenant out and all your good tenants will leave because of it. 

A lift station failed during the last hurricane. 

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.

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.