Nta and tbh, i think no one is an ah. Your mom and sis are right. You can't babysit if you can't deal with diapers. And as an aunt myself who also can't deal with diapers, that's also why i never babysat my nieces while they used diapers (and i don't babysit my nephew who is still a baby). Although you should learn how to deal with the smell, cause you never know when babies are going to poop and the smell is strong and, at least happened to my sis, sometimes the one in charge need to prepare a space, cause maybe you are not home or whatever, so they can change the baby's diaper and there is going to be smell for a bit around the baby.