@SimTrippy The game doesn't support hybrids. I had nothing but trouble with my alien-vamp as soon as she turned teen. Specifically with CAS, since both aliens and vamps have two forms. Outfits I made for her just didn't stick. As soon as I took her, or any of her family, into CAS, I had to do all her outfits again.
I also have a vamp/spellcaster (by cheats, though, since vamps can't ask a sage/other magic person to become a spellcaster) and I have no problems with him. I maxed out and got all the vampire perks/weaknesses before cheating his magic trait.
I don't know if its a bug or what, but simmers have always wanted hybrids, and Eaxis knows it. Aside from cheating, hybrids shouldn't be possible in game, since it isn't supported in any way. I feel there should be a check when a male sim is abducted, to check if he is any type of occult, like a vampire or mersim. If that check is true, then pregnancy shouldn't occur. Only "pure" human sims should get pregnant from abductions, to avoid frustration and glitches.
I do love my "mixed" sims, though. They're pretty fun to play, but as I said, had to remove the alien from my girl because of all the problems.