When they grow up a little more, they will want sewing machines! 4 grandkids means you need to keep at least 4 machines ... no fighting!
If you have extras to sell, craigslist is great. Keep in mind there are "money order" scammers on CL. Just delete the emails offering money orders and it will be all good. I think pricing at craigslist will be better than yard sale pricing, even for the worlds longest yard sale.