Parking - It depends on the B body you get. B's can be as short as 17' or as long as 24'(longest Mercedes Sprinter body). Check www.sportsmobile.com or manufacturers websites for size info. The widest is probably the Chevy. How long and wide are your legal parking spaces? You can probably rule out B+ and C RV's.
Accommodations - There are B vans made that will sleep 3 or 4 but there is a heavy price to be paid in terms of space for other features. The websites of B makers should show floorplans - look at those. Probably the best approach would be rear bunk beds that can be folded up. Sportsmobile and Advanced RV will build your van to suit. Check with them about bunk beds.
Probably you best option is to get a van that fits two and tow an Airliner or other small popup when there are more.