I had my sister ask about this for me on Reddit and someone commented on her post saying it would be a good idea to ask the question here. If it's alright I'll just copy paste the question as it was written on Reddit:

"Do these mods support the existence of hybrids whose two lifestates both have non-standard motives? For example, Vampire (thirst instead of hunger) and Mermaid (hydration instead of hygiene).

And how does the mod handle Alien hybrids (especially ones that have nonstandard motives from both the occult and alien sides)? Since Aliens are determined by DNA percentage instead of a simple yes/no status like Ghosts and Occults have."

Hi there. I believe the answer to the first question is yes, and on the second one a sim is considered an Alien if they have at least 20% Alien DNA. With less than that they may have some mild Alien-like appearance elements but not the full occult state, so that is still sort of a yes-no factor.

But let's not take that to the bank just yet. As fond as I am of hybrids, I've never played a Vampire-Mermaid nor an Alien in any kind of combo. It would be great if other players or our developer can confirm (or not) what I've said above.

Wow that was fast! Thank you very much, confirmation of some sort would be great.
I'm mostly just worried about how the motives are handled. Like, would such a hybrid just have one or the other occult state's motives, would it get both non-standard motives, or just have the needs of a normal sim?
I thought I'd ask someone first before experimenting myself because I'm a bit afraid of messing something up.

While we're waiting though, running an experiment on a test game or a copy of an ongoing game save off to the side would not be a horrible idea. Nothing that happens in such a game session that isn't meant to really go anywhere would affect the "real" ongoing saves.

I followed your advice and ran a little test with 3 sims. I probably should have made four but I think its safe to say Hybrid and Master Controller can handle these sorts of hybrids. The first two were a Mermaid and a Vampire. I added the other one's Occult life state to them and their motive bars turned the normal green instead of purple and blue. Both of them had Thirst and Hydration. Then with the third sim, a Mermaid, I gave him 30% Alien DNA. His motive bars remained the Mermaid blue, and he gained Brain Power in the place of Energy.

Yes, the purview of the mod is to handle the motives and interactions they should have as hybrids. They should have all the motives you'd expect them to have. The interface will do it's best to adjust.

I've never had these particular hybrids myself, but I have had fairy/vampires and fairy/mermaids and the mod works just as stated.

Happy to know it works for vampire/mermaid hybrids as well.

As for other hybrids, I had read that Imaginary Friends made real were unable to be changed to a hybrid of any kind. At least not with elixirs and I found that to be true as my alchemist was not allowed to throw an elixir at her nor was she allowed to use one on herself.

I never tried adding another occult to her via mods as that's not allowed in my current game.

So imagine my surprise when the Imaginary Friend made real's son married my fairy and they had a hybrid child!
I know it doesn't change their motive bars but still a welcome surprise and addition to my game.