Hi Phyllis!
It sounds like you will have a magical - and busy - trip to plan!
With the age ranges of your grandchildren, I think you should consider spending the majority of your time at the Magic Kingdom. So much of this park is geared to younger children and the expansion of Fantasyland has added even more to do!
The good news is that many of the rides at the Magic Kingdom will work for your group. Boys are sure to love
Buzz Lightyear's Space Ranger Spin will be sure to delight the boys - and your 9 month old can ride with you as well (win-win). For the Princesses (and maybe the Princes too) be sure to check out
Enchanted Tales with Belle. This new interactive story-telling experience lets the audience participate too - encourage everyone to volunteer to take a part in the story!
If the kids are early risers, try to get get to the parks at opening. If you can make a list of must-do rides for each child and knock those off first thing, then the rest of your day is all bonus!
Last but not least - Its easy to forget in all the fun, but Walt Disney World can be overwhelming too! There is so much going on - from sights and sounds to adrenaline to new foods. Be sure to try and keep to somewhat of a regular schedule. If naps are regular for this group, you may want to be sure to plan downtime in the afternoon. A return to the resort can give you all some time to relax, nap, or even recharge with a swim. You won't be able to do it all - to be honest, I still haven't done it all - so make sure to listen to the kids. Adjust to take them into account.
Hope this helps! I'd be happy to help with additional details if you'd like more help planning!