A BDSM relationship is something negotiated between two people. If the relationship includes play with more than one person, then each of the players needs to devise their own boundaries and dynamics, with each of the other players. There is no such thing as "The Dom" and "The Sub". Just how one person related to another. There are no rules about what works and what is right, except the basic rights of all humans, and the right to SSC and/or RACK. Google those if you don't know what they are.