So I figured I'd see what you all thought about these things:
1) Is there any non-sentient life outside of Earth-based life in the Alien universe?
The first four Alien movies and Prometheus don't really show us any indication of such -- only Alien Covenant shows a planet with largely Earth-like forests and plants and such. While any of the alien life was surprising to those in Prometheus, those in Alien Covenant don't seem surprised. My takeaway from this is that, while many worlds are essentially barren rocks or otherwise inhospitable (and thus need terraforming), by 2183, there are at least some familiar, hospitable worlds, and those are likely some of the few "paradise" worlds likely clamped down for the corporate elite. These places might also have been "seeded" by those like the Engineers, though I don't think that's a necessary detail to establish. Regardless, "natural" human-habitable planets are unlikely plentiful like in other sci-fi.
2) Is there any sentient life outside of Earth-based life and the xenomorphs (and their variants) in the Alien universe?
While no mention is given in Alien (outside of quarantine procedures), Alien 3, Resurrection, and Covenant (they specifically call out a lack of animal-type life in that), and Prometheus only had worms, Aliens implies something a bit different. Specifically, the Marines talk about being on "another bug hunt" as if this was something they commonly had to deal with (though in the case of xenomorphs, they're clearly not the sort of "bugs" they've had to deal with before). This leads me to believe that by that timeframe, alien life vaguely resembling non-vertebrates are at least not uncommon to discover, but nothing nearly as dangerous as xenomorphs, things fairly dumb and non-lethal but maybe tough/numerous enough to sometimes need military involvement (though this may just be a misuse/overkill situation as well). I'm uncertain what they might be, but I'd like to consider things equivalent to rats, emus, or other "nuisance" wildlife -- something like tribbles from Star Trek but more fitting for the Alien universe. It's also very possible that maybe "bug hunts" actually come purely from Earth-based insects that have carried over and somehow been mutated/genetically modified akin to killer bees, but that seems more of a stretch given that, outside of Prometheus, nobody in the Alien universe seems shocked at the idea of extraterrestrial life. Even if we consider "bug hunt" to mean a wild goose chase, there's still the overall larger sentiment that nobody in the first two movies seems shocked at the idea, even if they're skeptical of the details. I might try brainstorming some more specific ideas later.
3) Is there any sapient life outside of humans (and space jokeys/engineers) in the Alien universe?
Again, Prometheus marks this discovery as fairly special, but even in Alien, when the 'space truckers' come across a derelict alien ship, they don't seem terribly shocked at the idea so much as just calmly observing how it's unlike anything they've seen before. Aliens also makes reference to "Arcturians" which could well be just a name for certain group of transgender colonists (what I'd prefer to think). I generally think that the Alien universe, particularly after Aliens, establishes a precedent that there's no sapient life forms (alive) in the 2183 era aside from humans, and that even dead ones like the space jockeys/engineers are not plentiful. Still, this is the hardest aspect for me to reconcile, since on one hand, I think other sapient lifeforms would detract from what makes the Alien universe what it is, but on the other, find it a glaring issue that the first two movies seem to casually consider even sapient space-traveling life not surprising -- as if their universe might have a handful of sapient alien races that humans simply segregate themselves from mostly. What, if any, sapient life do you all think would be 'acceptable' in the Alien universe?
My intent for any games I run would likely be to keep things human-centric, with most worlds barren/alien/hostile in various ways, some 'terraformed' with maybe every 1 in 6 places having any sort of alien flora and other "biological" life, and maybe ever 1 in 66 places having ruins/remains of sapient life like the engineer derelict ship or the like, but no living sapient life. What are your thoughts though?