Welcome aboard! I've been a big enjoyer of aliens and part-aliens for many years myself, and AR is a lot of the stuff I've always wanted when playing with them! Starting a new save will give you things like my premade NPCs and also create a clean slate for relationships and things, but it's not necessary - you can cheat in traits where needed, and the rest of the traits and relationships will get filled in via normal gameplay. The mod will also randomly generate new sims in place of the premades.
I don't have a full list of cheats, per se, but there are a good number of hidden traits in the mod, trait_AlienDescendant among them. Yes, the alien descendant trait just signifies that a sim is descended from aliens - if a full alien has the descendant trait, then it marks them as a second gen+ sim (not from Sixam) and changes some dialogue options and buffs to be more appropriate. It's one of the systems that I was planning on building out a bit more later on. Part-aliens and full humans can also have the trait, but it doesn't really do anything for them as of v3.72 (part-aliens are treated as alien descendants by default, even without the trait).
The more interesting traits for your gameplay will most likely be the ones for the human sims - trait_KnowsTruth is the big one to add, for sims who know that aliens are real. There are also hidden traits around alien pollination and alien abduction - if the sim's been abducted in the past, if they know how to stop alien abductions, if they've decided they like getting abducted and want it to keep happening, if they've opted out of the whole thing, etc. And also if they've been pollinated in the past and know what pollination is. These hidden traits will be granted during normal gameplay and it'll be easier to have them be awarded during socials and things than to cheat them in since there's a lot of them and they're very particular (some things depend on which specific combo of traits your sim has).
In terms of the relationships - if you want your alien sim's human family members and friends to know they're an alien, then confessing to being an alien very rarely goes wrong, as long as friendship is high enough. Other ways of discovering that a sim is an alien have a chance to give a sim the Fear of Aliens if you're playing with the Fears system active. But even if they're afraid of aliens, you can Discuss Fears with them and work them through it.