It sounds like a neat trip.
Have you ever taken an RV trip before? If not, I strongly suggest renting one for a few days before buying. You will get a much better feel for things that are important to you in one, and some features to look for or avoid, and frankly how it suits your family dynamics. A year is a long time to spend together in a pretty tiny box. Then spend some time in the units you're thinking about and go through the motions of daily life: can you sit down to eat? cook and do dishes? switch the dinette or couch to a bed and back again? have room for schoolwork? Is there a place for the trash can, clean clothes, dirty laundry, and the other things you'll have to carry? Also look at the weight sticker to see how much you can carry without overloading the chassis; with five on a long trip, it will be a good bit to carry, even though some of the five are small people.