So sorry for what you are having to go through!!!
I'm glad that you have taken the high road and not retaliated...it only makes them feel better, like they are fighting the Devil himself! By being nice, they will think that you've got your life together and that causes more hurt than anything. They really want to see you having it tough, thus proving that you aren't doing good because you're not listening to Jehovah. It truly is a sickness perpetuated by the WTS. If you feel like saying congratulations to your sister through your Dad, go ahead. If you can't bring yourself to say anything, just let it go. By now your Dad has told your sister that you know....maybe wait and see how that plays out. One thing that I carry with me and remind myself of quite often, is something I learned in therapy. Deal with reality! Things are the way they are and deal with them on that basis. You can't deal with problems based on the way you wish things were...I know you wish your family didn't treat you this way, but look how they ARE treating you. Get a game plan together that is going to work for YOU and stick to it. It may be that you need to cut off contact with them, so that they can't get under your skin like this.....think about it, this could go on for the rest of your life. It may be that you can deal with just the occasional text from your Dad, but realize that he's not going to tell you family matters. Just some things to think about...I hate to see them mess with your mind...it's a delicate thing and you deserve better.
Swalker