a lot of people have unwanted sexual thoughts (intrusive thoughts) about people, even family members. While this could be a result of repressed abuse, there is no reason to jump to that as a cause immediately. It could also be the result of hypersexuality as a feature of some mental illness. Or the result of some other kind of trauma. or just intrusive thoughts.
If these thoughts disturb you, I strongly recommend that you speak to a therapist or counselor about them who can help you worth through what the origin of your intrusive thoughts might be.