In addition to the owner-occupant requirement, FHA is fairly strict regarding condition of the home, like must have working oven, flooring issues, age of roof, no moisture problems on door frames, window sills, etc.  

How many multifams have you owned in this genre, which we gently refer to as "working class".  

It's not uncommon, if there is a poor seal around the pipe, for moisture or water to run down the pipe to lower levels of the house.

There are some sources of moisture to the crawlspace that were known and a couple more I didn't realize at first, but all can be taken care of I estimate:    crawlspace vents maybe always left closed,  condensate drains for furnace and tankless water heater not run to proper drains, just running onto crawl dirt, no gutters on house and grading could be improved on one end of house.  

Wayne Brooks, I really appreciate your "gentle" response!

Regarding property liens, you should be notified after title search is complete, do your inspections (termite, moisture, maybe even a home inspection and get a written report) My preference is single family homes vs apartments/condo/townhouse unless it's at a extremely great price and factor in HOA dues....hope this helps.

They were happy (the hike was more gentle then they anticipated) and relieved (they would not be compelled to move).

My first question to you would be, "Where did the moisture come from to encourage that much mold to grow?"

Gentle persuasion, with a fast plan to ratchet it up if nice doesn't work.

I do know a little about mold, in that you need some sort of source of moisture to get it started, which we figured out was coming from the crank-out windows in the bathroom, which even though they weren't that old, were wood windows that had warped enough to let small amounts of water in during heavy storms.