Only bonded pairs should be kept together. You may see multiple rabbits in a single enclosure at pet stores, but those are usually just babies. Babies typically get along. But once their hormones kick in they will begin to fight (or breed). By 10 or so weeks of age, females should be separate from males. By 12-16 weeks, they should all be kept separate.
After rabbits have been fixed (spayed or neutered) they can be paired off. It is up to the individual rabbits as to whether or not they will get along. Bonding can be a difficult process and can sometimes takes weeks or more to accomplish.
Bonded pairs can share a cage. (Bonded trios or groups are more rare, but they could share a large enclosure. That would be the exception rather than the rule.)
So, in short, there should be no more than 1 bonded pair in an enclosure.