Congratulations on the twins, I totally expected Bebe and Uriah to adopt! I guess the hidden Simbot trait gets passed onto all offspring, like the vampire one (supposedly 50/50, pfft). I hope your save file turns out OK, I know my mummy hybrids got pretty glitchy in the end.
There is very little chance for a hidden trait not to be passed down. If there are two hidden traits (i.e. a Pizza Delivery girl and a Vampire have kids) the game is forced to choose only one of them. Hidden 'creature' traits (Mummy, Vampire, SimBot) have a high chance of being passed down. More like 90/10 than 50/50.
This percentage is getting higher with each patch, that's why most people never had a human child from a Vampire/Sim mix.
I too hope this save file doesn't get glitchy, I really want to see the girls grow up.