Petition to support polygamous marriage (when the system is released).

[Dhex]

Nunh have polygamist and inter-family sexual relationships (Father - Nunh, mating pool likely includes all sister/mothers of the Tribe; passes to sons -> Tia); Sunseekers are similar to lions - significantly inbreeding to root-out bad genes. A Nunh must either prove himself superior in combat or entice females away to have offspring. It can also be inferred that Tia that do not wish to become Nunh will seek alternatives - homosexual relationships or modern Eorzean relationships (marriage & monogamy homosexual or heterosexual).

Inter-species breeding is unclear - as of yet we (Adventurers) have not encountered any hybrids besides perhaps mixed-blood Garleans and the divergent Padjal (a sub-species of Hyur Midlanders).
Off-spring of mixed blood are likely possible but highly unlikely due to extremes of sexsiual dimorphism and adaptation among races; in example Roegadyn are very unlikely to comfortably maintain a healthy sexual relationship nor conceive a with a Hyur/Miqote/Lalafell without significant risks - Miqote females have significantly wider hips possibly because the likelihood of twins or triplets is higher among both Sunseekers & Moonkeepers.

Given this the foundation for the possibility of acceptable polygamy lies only with traditional tribal Sunseekers; female tribe members however are not bound by law only by an arrangement based in tradition. This tradition also implies that the Nunh of a tribe passes by combat, or by blood inheritance and must be approved of by a majority of the females in the tribe.

These principles withstanding I believe that it goes against the legality of an Eorzean Union to be shared among more than two individuals.