Some experience

The package is not bad for first time expaitrac. If your elder son is not in 11th grade, relocate all your family to Shanghai. It is great opportunity for your hubby, two children and yourself. Keep one thing in mind, all the pressure is on your hu*****and. It is very tough to re-enter to chinese life after in Northern Americ for so many years(no kidding). Your hu*****and absolutedly needs u and his kids around him not separated by Pacific Oocean. The most important thing is confidence. If you don't have, kids won't have too. Your kids should understand that DAD BRINGS HOME THE BREAD. It is time for them to support their Dad.

Your family should have a trip to visit Shanghai before relocation. FIND THE SCHOOL FIRST, THEN THE HOUSE. Try not far away. For after school actives I am sure you and kids don't want to stuck into traffic jam. But the main challenge is: there is not so many good international school with American curriculum, maybe one or two but usually there is a long waiting list. You have to shop around. Don't try to change to other curriculum. It wont wok well for high schoolers and waste time.

If possible ask the company to arrange an agent for assisting school and housing. It is very helpful and saving your time. Actually They are also the window for you to re-adapt modern Chinese culture and life.

One tip for school visiting: be modest. They didn't send invitation to you. It is parents who want their kids to attend their school. These private school always think they are very best in that region. They think the private school always out-pace average public school... Anyway don't make them unhappy, even you feel upset.

After finding the school, try find the house nearby. This is one of the way to negotiate the housing allowance, because family have to live in that area and must be comfortable for your family.
Keep in mind:
The school tuition will directly pay to school if your children attend. It does count as your income on w-2, but company will pay the tax, so don't worry about it. However, if you decide not to go, you do save a lot for company. But not add a dime on your hu*****and's paycheck.