This series is about the joy of worldbuilding. I didn't quite think I'd spread this out into so many posts, but I guess I have a lot of joy to talk about!
Human beings are far more interesting than one might think given the ongoing social pressure for individuals to conform to the American ideal: the heterosexual, monogomous nuclear family (or, gosh, now, even simply the monogamous nuclear family). I have to say that I think that "ideal" is about the most boring thing human beings have come up with in history (and human beings have come up with a lot of interesting and different relationship structures). And the ideal that there should be only two gender expressions: masculine men and feminine women, is also pretty boring, at least for me (and historically, things have been quite a bit more interesting than that.) Therefore, unlike most speculative fiction, the characters and relationships I most often explore do not fit these ideals.
Humans are pretty much always the main characters in my books, even though aliens are certainly a presence at times. And when it comes to humans, I often start with one fundamental idea: what if we created relationships between people who were free to express their gender identity as they choose, and free to choose whover (and how many ever) they wanted to? What would those relationships look like, and how would society structure itself around those relationships? I think that is core - as a society, we do arrange ourselves largely around the family structures we create - so if the structures were radically different, then the resulting societies would have to be radically different.
One example is the Casitian system. Casitians are basically single, except for a period of about 15 or so Earth years, where they have, and raise, children in a family group if they choose to. An individual Casitian who wants to raise children finds an opposite-sex partner that they think will be a good match for child-rearing (no romantic attachment is expected or encouraged.) Eight to ten adults form a family group to raise their children collectively, until the children reach the age of about 12 or 13. where they leave to join a youth community. Before and after this period, or if someone chooses not to raise children, Casitians live on their own, and most spend the winter (which is actually the equivalent of a year on Earth) living with a "companion" (read: romantic partner), of any gender. This is sort of a modified gender and sexuality fluid serial monogamy model.
Then, there are the Trageri. This is in a book coming out sometime later this year, called "Becoming Queen." The Trageri have one of the more interesting relationship and family systems. I think it's kinda cool, if I do say so myself. Trageri (one of two nations, the other nation does not at all share this system) is a monarchy organized in "houses" - and each house has anywhere from thirty to sixty family members, as well as another thirty to one hundred or (many) more affiliated employees (and that number depends on the wealth and influence of a house.) When the eldest female of her generation comes of age, it is her duty, as head of the house, to find eight to eleven spouses, who will collectively raise the next generation of the house. There are often romantic attachments between these spouses (some can come from the same house, as there will be children unrelated to each other in the same house,) but the primary function of this process is to find others who will keep the house strong, and do well to raise the children. Individuals are free to have romantic relationships of any kind outside of the marraige, as long as they are exceedingly careful about birth control (if necessary - queer relationships are fully accepted.)
When it comes to aliens, I've basically taken my cue from the amazing variability in gender, sexual expression, pair-bonding. and young-rearing that exists on this planet. There are organisms on earth that change their sex during their lives. They were the model for the Kurool, who change sex several times in their lives (although they do it consciously.) Some male animals take the lead on rearing young. The males of the aliens I'm writing about now, called the Eeriv, have a pouch on their back where the young live, and glands to feed them.
I do have one alien species, the Tud'scla, who have five individuals who contribute their genetic material to their offspring, something not found on Earth (that I know of.) The Tud'scla are pentaploid (that is, they have five sets of chromosomes). There are no sexes or gender in this species - individuals can both contribute their genetic material to one who will incubate the eggs, or they can be the incubator.
Gender and gender expression (or the lack thereof,) sexuality (homo, hetero, bi, pan, etc.,) and relationship structures (monogamous, polyamorous, etc.) will have foundational influence on society, and that is really important (and fun!) stuff to explore. And it's also always important to think about ramifications of these structures, and the kinds of conflict that can arise because of them. Great fodder for plots!