If your partner has done something that hurt you like cheating for instance, that's a matter between the two of you, how your child feels toward the other parent is for them to decide. So it is incredibly selfish behaviour to tell bad things about your former partner to your child when these thing affect only you. The same thing applies to the family members of your partner. My uncle's prick of an ex frequently bad mouths my grandmother and other family members to discourage my cousins from spending time with us and it really pisses me off to a whole new level, if you think a family member of your former partner shouldn't be around your child for safety reasons, then you should talk it up with the child's other parent, and if the other parent shouldn't be around the child for safety reasons, than you should talk to your lawyer