Sex and Gender

A'Viltrians, Rheans, and Tuhntians have 6 individual sexes and a really relaxed view of gender, making it impossible for anyone to be straight... except perhaps the Queens and Kings but anyway. Alls I'm saying is that these aliens are gay. These are gayliens. ALRIGHT Are you ready to delve into the world of alien biology? Let's do it.
Most closely related to the marsupial mammal, A'Viltirans, Rheans, and Tuhntians are egg-laying species and frequently have large broods which they never interact with. Everyone's raised in large, sprawling families under the same Queen.
Panseen and Udonians CAN mate with Tuhntians and Titians (with difficulty) but not Rheans or A’Viltrians.
Generally, Tuhntians have either a little Udonian in them (i.e. Xan and Aimz) or a little Rhean in them (i.e. Precious Butler).
Titanians are an offshoot of Rheans who bred with Panseen at one point and bred themselves for extra limb and eye mutations because if two is better than one, six is better than two.

Designations

Ones These are your Kings, Consorts, or Mistresses. They've only got the one pelvic ridge and they really only have the stuff for laying eggs. Not a fun job. Most ones masquerade as twos.
Twos Typically more on the masculine side physically, do not reproduce.
Threes Smack in the middle physically, do not reproduce.
Fours Smack in the middle physically, do not reproduce.
Fives Typically more on the feminine side physically, do not reproduce.
Sixes Typically more feminine, most desire to be Queens because it's an easy and highly regarded job, but some will masquerade as fives if they're uninterested in the lifestyle.

List of Character Sexes

(Because, obviously, you want to know.)
Ones King Hyctar, King Syko, Mistress Selectri
Twos Precious Butler
Threes Yvonne of Rhea
Fours Xan of Tuhnt, Aimz of Tuhnt
Fives Sonan of Tuhnt, Listay of Rhea
Sixes Queen Rapite, Queen Vorcia, Queen Carmnia, IX of Rhea