Also, I have seen seminars how to rent from others and rent back for Air BnB etc.You can check with legal counsel in this regard.

Home depot rents a Hepa air scrubber, I will ask them about it

@Matthew Truty you're in rarified air brother.

There is a ceiling fan in the bathroom but I have a feeling they aren't using because it's generates cool air.  

The major project to be done will be to replace knob and tube wiring in two of the four apartment units (the 2nd floor and 3rd floor of the building).I'm looking to connect with other local investors or contractors who have had experience working with knob and tube in the past in the Philadelphia area. 

I replaced the furnace and added air conditioning in the house I currently live in in exchange for rent, and I’ve replaced a condenser in lieu of a deposit.  

and they connect a plastic flex corrugated  4" duct into your attic and vent humid hot air into that space?

I've got a lot of balls in the air this year (1) my IT job (2) first year as a Realtor (3) and this project -- I'd say just lowering my expectations on how quickly I'd finish would have been a good start.

@Lisa Foreman someone like a SERVPRO could tell you mold condition if you don’t know or trust anyone like that you could have an air quality test done.

One even said "thank goodness our condo didn't have the Nest system so we could actually control the air."