Just to update this a bit. We've got some now and while we've yet to check and confirm their status as hybrids they seem to be doing well together. We got two, found them unhappy away from their littermates and had bought the other two within 24 hours to see if we could successfully reintroduce them after such a short time apart (if we'd taken longer to realise the boys were unhappy we'd never have tried a reintroduction). Did make sure we could manage an extra cage before we bought the second pair though, since we knew there were no guarantees the boys'd accept each other back.
We put the carry case containing the newer two into a big box the others hadn't even seen before, put the two we got first into the box in their food bowl (then both groups had somewhere they did know a bit) and opened the carry case.
The reintroductions went fantastically, they were all thrilled to be reunited and the boys have been much happier since.
We've since realised that the pair we chose was an unfortunate pairing of one of the independant boys and the one who cares most about knowing where the others are. Wasn't really a great idea and having all four is working really well, they routinely sleep in a heap together and have taken great pleasure in setting up about six different beds in their cage. When the boys are asleep we usually find that at least two are sleeping together, and who it is can vary a lot. We've also found every other possible combination of pairs/trios sleeping together, and we often see them sharing things, even when they don't need to. (We've also got one who seems to love waking the others up by climbing over them, and they all take that fine too lol)
The original questions.
We're housing four together.
Got them from the pet shop.
We don't know if they were together from birth or introduced by 5-6 weeks when the pet shop would have got them.
The cage is approximately 85cm by 75cm, its also about 30cm deep.
They've got four flying saucers at the moment.
We're using a rabbit sized food bowl, but are prepared to remove it if neccessary.
They've got four water bottles.
They've got four plastic houses (same shape and size), and one made from a cardboard box (we're also prepared to remove that if neccessary).
They've got a lot of toys, but four of each, and only one sand bath at the moment, but we're prepared to place more (identical ones) in the cage if needed.
They're only about 12 weeks so I can't guarantee they'll stay together but thought I'd let you know what we've got so far. They've been separated for 24 hours due to buying two and then getting the rest of the litter when they seemed unhappy about the separation. We haven't seen them play fighting yet and we're confident they get along well, partially because of they got distressed about the separation, partially because they spend so much time sleeping together and sharing things when awake.
If this goes as well as we hope, I see no reason to avoid them in the future, but we're not planning that far ahead now. We hope to have this lot for a while yet anyway