I'd wait to take the buyout. You'd also get the benefit of the improvement in the market, even though you have a good amount of equity in your home now.
As for your eldest, why not send her to live with your extended family so that she could start high school there in the fall since it is the family's plan to move anyway. High school is just a tough time to transition, but it sounds like the size of the school and the support of her extended family would make this work for her. My cousin and I lobbied our parents for me to go to high school with him (which would have required me moving from New Jersey to Chicago), but, our mom's didn't go for it. My mom had no plans of moving to Chicago,
, so, I see as an adult how that really didn't make sense in our situation.