advice on kit

As I have a large extended family I have a few problems with acomidation Theres 4 adults 1 teenager and 2 todlers , plus Ive got a list as long as my arm as to what my wife wants in a caravan. The eaysiest way i can see to get around the acomidation is to build a large day van thats got enuf room for transport purposes a double bed for the grand perants and a bath room ( with a proper toilet on the wifes demand list ) and then tow a 6 berth caravan is this doable legally and will I have trouble getting access to sites as Ive been told alot of them dont allow vans

sorry for the long winded post thanks for reading