The family member has held the buildings for decades and managed on his own, but he is 80 years old with health declining and cannot properly manage them anymore.

If you decide to allow it, I would add an addendum to the lease stating the rules and possibly getting a pet deposit.

Guidelines to follow:Only buy in low-cost markets if your costs stay under 75% even after paying for two major capital improvements, such as a new roof and a new water service line.Make sure you can eliminate all obvious safety and health hazards—like broken sidewalks, missing railings, lead paint, or poor lighting.

Without knowing the total picture (goals, income needs, tax bracket, heirs, health and so on) the seller could put together a properly structured long term lease option, that should do the trick.

A properly installed radon mitigation system with post‑test results under typical safety thresholds doesn’t devalue a property; if anything, it reduces a future buyer’s objection by turning a health risk into a solved, documented feature.

After looking through the past threads regarding senior housing it seems like it is a very difficult market to enter due to the need to essentially be a health care provider.

( difficulty reselling the unit, and it has a small percentage risk on your health)I would like to know if the value of the condo will decrease overtime and your thoughts about the situation.

.- These are actually pets the applicants are trying to avoid paying additional pet fees & rent for.

I like to do that too - it helps save you and your applicants time if they're not a good fit - for example, they have a pet and you don't allow pets or they want a 6 month lease and you only start with a 12 month lease. 

You could only evict for health and safety reasons.