I crate 4 of my 5 while I'm out. All of my dogs get along, there has never been a scuffle, but I know that if something were to come up that I could possible loose a dog. Tinker is soooo small (well under 2 pounds) and Tia isn't steady on her feet anymore so I also worry about accidents with the stairs.
My dogs truly love their kennels and I never leave for more than a few hours so I'm very happy to kennel them when I go.
Tia and Tinker kennel together and Amos and Lola share a kennel (usually) so they're certainly not lonely.
Sophie has the run of the house except the bedrooms...she just sleeps anyway.
I do recommend to many clients that they seperate their dogs. Not long ago I was at a home of a client with 3 Jack Russels. They had always been fine with the cat and were all left out together, never an incident.
The owners called me in when they returned one day to find the cat had been killed and partially eaten. All three dogs (mother, now spayed, the altered dad, and female 2 year old pup, also spayed) were bloody.
Often times it does come down to breed and of course individual dogs but there are breeds that I would never leave together due to predisposition for d/d aggression and preditory drift (as in the case of the Jacks). I honestly wouldn't leave most terriers out together or with access to other animals.
Many, many multiple dog family's do well left out all together. It really does depend on the breed, individual temperments and the dynamics of the group.