Do not put that clause in! She can renegotiate anyway, but this makes it more solid. Who know what will the siutation will be in 2 years? If she wants to move away then she can let you have full custody.
Have you thought about getting counselling for your children? They really seem to be grieving the loss of their little worlds, quite naturally of course.
My heart goes out to you and your children.
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim