Re: in-laws visiting, vent
Co-sleeping on an air mattress isn't really recommended - it would be fine if the mattress stayed totally firm all night, but usually they deflate somewhat and get squishy. Just too risky.
Sounds like a tight squeeze, no matter how you move things/beds/people around! Is there any other family close by that they could stay with?
When we lived in our apartment (2bdr, with DD and DS1) and small house (again 2bdr, with DD, DS1 and DS2) we would just have family sleep in the living room. It wasn't really a big deal for anyone, even with them not having a "real" room. They just had to deal with DD jumping on them when she got up in the mornings!