AnathaShesha
So personally I would like the maid to become a wife. But if you are only thinking about adding another wife because of his children/origin parts. Then you don't really have to since you have added a loop hole without realising it. Since Tartarus is a place instead of a creature, even if it is a sentient place. You can have it take the form of a sentient weapon, or a spirit like entity in Abaddon that stores the excess powers of his other origin parts. Then explain it with how they are different from there (siblings). For example, it can store the excess powers perfectly because it is/was the prison for the powerful monsters/beings made by the gods, and its sibling Typhon.
@AnathaShesha In my opinion, Tita is locked by what Abbadon promised her earlier. However, the Phoenix Queen (name blanking rn) is ranked high to be a wife... my suggestion is either Tita and the Phoenix Queen become his wives, or in a really cool/chaotic twist, have Tita and the Phoenix Queen merge/combine into one intity to spice things up and close both romantic interests at once...
yo i hate to be THAT guy, but we all already voted and the majority was WELL in favor for tita at least, and im sure it would be the same for erica, if you need to add more wives ADD THEM, there is literally NOTHING WRONG with adding more wives as long as its organic and goes with the story, as long as he dont start collecting them like pokemon, nothing is wrong.
Twins, or letting a wife give birth a second time, would resolve it. No need for an extra wife just for that. Story wise it also feels somewhat off to be add another wife at this point, now that they've hunkered down and all that. Unless it's perhaps someone he meets in a future trip, like a godess or other divine entity? But even then I don't think there's any need for another wife, the current group pretty much provides everything you need.
the story is already greatbecause you dont force things. its not like he would pick a random woman anyways. if anything it should be his wives telling him to add another because she has done somethinf worthy for them. a supreme goddess thats imprisoned in the gods realm and helps him would def be a cool idea