Personally, I think the most successful way is to focus on only two bunnies at a time. So maybe do sessions with bunny A and bunny B for a couple weeks, then switch and do bunny A with bunny C, or bunny B with bunny C. I wouldn't bond them to the point where they have moved in together, but I would definitely get each pair to a fairly drama free point before you try them all at the same time. You can try all three together at once, but I think it would be pretty overwhelming and potentially explosive if one or another was aggressive at first.