Continuing the "Space Empire played as a CK2 character" thought, this means:
Most empires are female, or the alien'y equivalent.
Or possibly hermaphroditic, as you can apparently impregnate yourself and have children.
But it might have been science that actually got you up the duff. Science didn't use protection when it was with you either. Or bother paying maintenance. But it still does things for you like fix fences and make sure the electronics in your house all work.
Or did the Post-Sambos come from god? Immaculately. To wage war against the galaxy?
All reasonable views to RP a successor species in Stellaris.
It'll be good to see how deep the diplomacy system goes to see if there are family and marriage analogues in there. But if you view an empire as a noble from CK2, it's already looking deep (and possibly somewhat disturbing). Plus, you'll get to pick or make your own family, but it doesn't sound like you start out with relations.
It might not be too hard to force-gen "You are the Post-Post-Post-Foo, son of Post-Post-Foo, brother of Post-Post-Post-Foo2, great grandson of the Foo" in a mod, thereby giving you immediate "family" lines and relations already in place.
It depends on whether you can have more than one gene-modification event per race, or if you're stuck with one and then pre-sentients are your only outlet for more "family". I don't see why there'd only be one though. Dump some colonists on a world too hot for them, some on too cold, some on a high grav world, some on a high radiation world, and they'd all want to gene-mod themselves in different ways I'd expect. This actually makes the worlds themselves a "father" analogue for this scenario.
I wonder if there'll be any automatic bond or hate between any of the Foo line. And how many species you can uplift for family "lineages" of your race.