I would seek genetic counseling to see what your risks would be. What type of disability do they have? My sister has mental retardation bc of lack of oxygen at birth. So hers was brain damage technically. So she could have a normal kid.
I don't know if its the case with all disabilities or diseases but sometimes you can have a disability but not be a carrier or be a carrier but not have the disability. I know a girl who passed away at 26 due to cystic fibrosis but was not a carrier however her parents both were so that's how she ended up with it. However her daughter did not get it from her. I think its something you should ask your dr. But adoption is always an option if you don't want to risk it however there is always a risk that way also. Maybe they can do blood work or something. Good luck to you.
It depends on their disability but it could make your chances higher