"Uhg, Family" moodlet?

@Andipoodle , thanks for your detailed description of your problem! 🙂  As far as I know, the only "jealousy" programed into the game is with the Jealousy trait, but its description only lists it as pertaining romantic jealousy ... also, my experience of it in the game has only produced results for romantic jealousy.   Also, there does not seem to be a knowledge of "birth order" in the game.  Even with the Parenthood Game Pack, I have not run into any birth order issues so far.

I think the most likely culprit is his low Emotional Control.  That would make him more likely to deal with any negative emotion in an unproductive way.  (I don't know if it would make him get angry more often, though, nor do I know if it would make him get the "Ugh Family" moodlet more often).  Try to raise his emotional control levels and see if that helps!  One good way to raise emotional control is to go into Buy Mode and buy a journal for him.  Have him write in his journal often, and that will raise his emotional control! 😇 Other actions will also raise emotional control, but I don't remember all of them, and the journal is easy to use and not expensive! 😉

As for the uncontrollable feasting on people even when his thirst meter is full, that sounds like a separate issue (but I could be wrong).  I'm not sure what could be causing that!  🤔  The only thing I can think of is if you have Mods or CC (Custom Content) in your game.  That could be affecting both the "Ugh Family" moodlet, but is very likely to be making your Vampire Sim constantly drink from other Sims even when they are full.  What Aspiration and traits does your Vampire Sim have?