I've even thought about getting a SF and possibly air bnbing the rooms out as well. 

Two of my vents arent getting air pushed through them from the AC unit (7 other vents are working fine and receiving air and the AC system works fine).

With the windows open, it helps circulate air more of course but doesn't do much of anything for the humidity levels.

Check air rights and density.

Cheers,Daveyou will pay big money but a licensed air bnb in Charleston will beat any rental anywhere in the US hands down. 

Air Flow - There is a window in the room and I have been advised that an AC unit can be added to this to keep the room cool2.

Improving the building envelope - air sealing, greater insulation - will give you more bang for your buck.

Personally, it doesn't bother me if my kids sleep on a futon or sofa bed,  but if I had to pay extra for 7 people and then they gave us air mattresses I'd be a little annoyed. 

Just curious how you go about having the discussion with the landlords about using it for air bnb?

I doubt that your road should be the same as mine, and I think you should spend some time coming to grips with what's best for your market and what's best for you. well in Pacifica you would never run your air conditioner.. matter of fact you would never need one..