Cannot edit preexisting sims

So, I use my sims to do social testing for a book I'm writing. I'm too lazy to actually get a sim pregnant, so I just adopt a baby and once that baby needs to be aged into a toddler, I go into create a sim and use the genetics tool to make them a kid, then I replace the baby with that toddler I made in Create in a sim. Problem is,I didn't replace the parents already in the game with the versions of them I used in create a sim. (I basically went into create a sim before entering live mode, in other words, I entered create a sim instead of selecting a household to play, and since they were saved in my library I selected them from there and then used the genetics tool to make their kid. So technically she's not the daughter of the parents I have in the game, she's just their roommate who looks identical to them. The only way I can make the toddler their bio daughter now is through entering create a sim in live mood. I have the cheat Cas.fulleditmode on and it's letting me do everything but make my sim their daughter. I can only make her their sister or roommate and both sims are adults.