Families with AS in them are different in many ways. Unfortunately IMO these quirks come part and parcel with the person you are with. He does need a life of his own and if he is AS he will need help with that. With his AS it is easier for others to triangulate which is what the sister seems to be doing. IMO the intensity of your reaction is going to make things more difficult. You can't change them you can only change you and your reaction/response.