If you can afford the trip over Christmas, it's wonderful being there over the holidays (I was there over Christmas this past year). That's a BIG if though. It is significantly more expensive between Christmas and New Years. Last year there were room discounts right up until 12/24 but they did not extend beyond. Those of us that could arrive earlier got
free dining but we had to begin our vacations by 12/17 meaning the kids missed a few days of school. I'm guessing that's not an option for your family being teachers. Magical Vacations Travel did have some really good room only discounts for the week between Christmas and New Year so at least that's always an option. You won't find any Disney discounts that week but MV will probably have something though they only offer rooms at select resorts and you can't buy a dining plan with their discounted rooms.
We're northerners so summer in FL is hard on us, but with you being from Alabama, I would think you might not enjoy the cooler weather in December (for us it was nice but I bet southerners were freezing).
Have you ever travelled with these grandparents before? I know it just wouldn't work out well with either my parents or DH's parents but some families have a great time doing this. You need to think about what differences there will be in your vacation with or without them and decide if those are differences that you want or not (besides just the babysitting).
