There's not enough space between the beds, but there is plenty of space between the one bed and the window. We've had a queen air mattress there with no issues. A pack-n-play will also fit in the bathroom under the shelf.
Ok, so it can fit in the bathroom, in the "closet" area? We're trying to come up with a place where we can put our 3 year old down in some privacy, and still be up watching TV or playing card games at the table. So if it's in the closet area(even if it sticks out to be in front of the sink a bit) we could even close it off at bedtime!