If we're talking indoors, in my opinion 8 bonded rabbits living all together would need a room, not a cage. You could build an NIC cage, but by the time you make it big enough to accommodate 8 rabbits, it's probably going to take up a large portion of a room anyway. It also depends on what size rabbits you're talking about and we really can't make any conclusions without knowing that.
Trios and duos, again, depending on size. For a duo of medium sized rabbits, I would say for an NIC cage, 4-5 grids long, 2 wide and 3-4 high (with two levels).
A trio of something like nethies could easily fit in a condo the same size, but if you're talking large breeds, you need something at least 5 or 6 grids long and 4 high.