We have a spare double in the guest room and a few swags that can end up on floors as required. We have a double foam mattress that we use for camping. We will probably re-install the loft bed in DS's room when he's older or possibly put it up above the double to fit in families of guests.
The most extras we've fitted in has been 8 as well as us........not much floor space left then in our small 3 bedder!