First you should take the class. I presume there is time on the water. Although 3 hours away, Charleston is bound to have some rental boats..perhaps you can take the course there and carry the family along on the water class. Check online for sailing schools and rentals in Charleston. As far as your family concerns....start sailing on a lake. It will be less threatening, give a safe opportunity for practice, and almost no one gets sea sick on a lake. You will find plenty of challenges.
Regarding a boat and cost..There usually are many boats 23-25', vintage 1983 for no more than 5K. If you take care of her and make a few improvements you can sell the boat for about what you paid. With a family I think you might want an older boat of this size. You could also look for a 22' daysailer for a bit less but with less room. There is no substitute for talking with a person who sails a lot. You can find them and they will talk. Ask to go out with them and take your family if possible. Happy sailing!