It may appear as a happy relationship to the outside world but I believe it will always have its internal jealousies. Whether it is one Dom/me with multiple subs or one sub with multiple Doms/mes I can't see it happening without serious jealousies occurring.
That depends on the people. Some people can operate on a jealousy free basis. It depends more on self esteem than anything else. (IMO)
[One of the reasons I prefer self-confident subs over humiliated subs.]