Re: Radiation exposure
There would have been no risk to your family as long as the proper tracer dose was given. (Mistakes do happen, we all know.)
In the RAIU test, only small amounts of radioactive tracer are used. The tracer loses most of its radioactivity in hours or days and is quickly eliminated from the body through the urine. You should have been instructed to flush twice for a day or two, and to thoroughly wash your hands after toileting. They wouldn't allow people to leave the facility if they were strongly radioactive.
It would be my bet that your daughters have just inherited your bad thyroid genes, and that your uptake scan has nothing to do with their conditions.