Okay before we going into discussing what should we stick in to the lore I'm going to jot down some ideas and form a Lore road map that will use the following source materials as guidlines (Predator, Predator 2, Predators, Prometheus, Alien Covenant, Alien, Alien isolation, Aliens, Alien 3, Alien Colonial Marines (some parts), Alien Resurrection, and some of the expanded universe's AVP (Comics, Novel, and Games only) and EU Alien as long as it doesn't directly contradict the Alien films.

Okay we got the X1 Xenomorphs out of the way as they are the justififaction on why we have playable xenomorphs.

The time peroid will be set a while after Alien 3 but way before Alien Resurrection. So we can make use of the Weyland-Yutani coporation before its Wal-Mart buyout.

Xenomorphs and their relatives:
Hammerpede,
Trilobite,
Deacon,
Backburster/Mouthburster,
Neomorph,
Facehugger,
Chestburster,
Protomorph,
Lurker (represented by the Xenomorph from ALIEN),
Warriors (represented by the xenomorphs from ALIENS),
Queen,
Royal Facehugger,
Runner (represented by the xenomorph from ALIEN 3),
Queen Chestburster,
Genetic Drone (Represented by the xenomorphs from Alien Resurrection),
Queen Mother,
Empress,
King,
Predalien,
Xenoborg,
Royal Guard,
Preatorian.

The Yaut'ja (Ya-oot-cha) will retain alot of their expanded universe lore.
Heirarchy rank levels are based on honor:
Badblood
Untouchables
Unblood
Young Blood
Blooded
Honored
Elder
Arbitrator

Engineers should have a ranking system similiar to the predators but rather than being based on the hunts and honor it should be based on how much devotion they have for their creators or goals.
Peasant
Initiate
Adept
Acrolyte
Monk
Priest
Bishop
Archbishop