Finding a hutch for 5 guineas, I think I'd rehome the DH 
I will try and work out what space they'd need ( going by the 4'x2' for 2/ 5'x2' for 3), you'd need something like 14 square foot , most hutches are 2' wide.
You could get a double decker if your hogs are likely to climb.
My lardies like Ground Floor Living, they have a recycled wooden playhouse.
They have the floor area, it's light (4 windows, 2 can be removed and have the inner part re-inforced with wooden bars, heavy metal mesh,and flymesh)
You can insulate them, hay is excellant to keep them snug.
Snugglepads.
Cardboard and newspaper.
Fleece.
Main problems I've found though
Damp and draughts.
Extremes of heat and cold.
Going from hot-cold or cold-hot.
My pigs are in at night for winter and go out to their Pighouse by day (we clean at night, so in winter we put the fresh bedding in early morning, put their heater on and let it warm up before they go out)
At the moment (they are out) they have a low heat overnight.
5 piggies will snuggle (hopefully) but you'll need lots of hidey spaces and boxes.
Could you get a shed on Gumtree or similar then customise it? You could put a hutch inside for sleeping then lock them in. Keeps them fox safe.
Otherwise you need to get waterproof covers for the hutch.
My piggies would insist that you build a raised bed for grass BTW
, just for them.