Camilynns,
Welcome. I have not had surgery, but am an adult living with slowly progressing curves and pain.
If your fusion is what you say it is, I don't see why you would develop pain. Are you in pain now?
If you are in good health, I don't see why this would stop you from having kids when the time comes. It would most likely prevent you from being able to have an epidural for labor pain management. You would have to talk to your OB/GYN about a C-section or vaginal delivery depending on if you have iliac screws. But you shouldn't let that scare you, either. Some of us that aren't fused have ended up having C-sections. Healthy baby is the outcome you want. I would also mention it to the pediatrician since you AND your sister were both fused. That way your child/ren could be watched. There's so much that they don't know about heredity and scoliosis.
Final advice: If you are that concerned over future pain, I would take Pooka1's suggestion and go see a surgeon for an x-ray and a check-up. It would be good to do anyway since you haven't seen anyone for 12 years. My guess is that IF you are NOT having pain now and you truly are fused to the pelvis, I wouldn't expect any problems. If you aren't fused to the pelvis OR are having pain, it would be a good idea to see what's happening in there just to check it out.
I think most of us are limited to some degree (excluding Titanium Ed). That just comes with the territory.
I have a daughter-in-law that is fused from like T2 to L1 or L2. She had her surgery at 16 years old and is 23 now. She is having some pain below her fusion. I think it's mostly hardware related where a long piece of rod was left and irritates the muscle. She also has some lower back pain once in awhile. She is very active, though. She went skiing the other day. She would never bungee jump or sky dive, but she does pretty much what she wants to do. She has some of the same anxieties that you do. Enjoy your life now. Old age brings pain no matter how healthy you are when you are young.
Take care. I'm glad you found us. It was a relief for me to find others to talk to, also.
Be happy!
We don't know what tomorrow brings,
but we are alive today!