I have never liked having my arms inside a sleeping bag, keeping them out gets a bit cold too so I have always used a cheapish sleeping bag and a blanket over the top(it's a thick fleecy blanket and is really warm).
I would also suggest single sleeping bags with either a duvet or large blanket over the top.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.