Male rabbits (bucks) kept together will most often fight once sexually mature, although neutered bucks will live happily together.
Female rabbits (does) will live happily together if introduced at a young age or carefully introduced at an older age.
A buck and doe should not kept together as this will result in continuous breeding. Even if the intention is to breed at some point, the buck and doe should only be introduced for a short period for mating to occur and kept separate at other times.
Although rabbits and guinea pigs will "accept" each other as companions, the habit of a rabbit to playfully jump when happy means that its powerful hind legs can cause serious internal injury by mistake to a guinea pig companion, that could result in death. This is the case with even the smallest of rabbit breeds. Rabbits and guinea pigs also have different dietary requirements and different means of communicating. Therefore rabbits should not be housed with guinea pigs and the best and most natural companion for any pet rabbit is always another rabbit.