Hi, A.. My heart goes out to you. My husband and I are in a very similar situation. We both owned homes and we have been making double mortgage payments for two years. The market is so bad where we live that we can't get out from under either house and it is killing us financially. He is very devoted to his family, who treated my children like outsiders. That got so bad that my youngest used to beg me to leave him home alone rather than make him go to their house (he was 5 at the time).
It is horrible to be pulled in so many directions, especially when you love your husband and want so much for your kids. It's easy to say "Why didn't we.." or "We never should have...", but the fact of the matter is that you are where you are. The only advice I can give you is pray about it and then decide what you want and what the best course of action is. Make pros and cons lists if you have to.
If there are jobs for your husband where you are and the general economics are better, rent our your old house and stay in the new one. Even if you can only rent it for a portion of the current payment (based on the market), it's that much less you have to come up with. (However, if you rent it, avoid the problems and hire an agency to handle it - in my town it costs 10% of the payment amount and they take care of all repairs, collecting rent, eviction if necessary, etc.). You can only do what you can do. If you end up losing your home, it's about 2 years before you can purchase another home. If you've been a faithful tenant and the landlord also has multiple homes they are trying to sell, they may be willing to give you another year or two on your contract to get your credit back up and purchase the home. There are lease options and other things you can do, but make sure you talk to a financial advisor so you know all the ramifications.
If you are going to make your marriage and your family work, you need to be together. However: One thing you HAVE to consider is that you are your children's advocate. No one else is and they are dependent on you to make decisions that are in their best interest to promote a healthy, happy and secure home and environment. If they are unhappy because they are treated poorly by your in-laws, you have to do what's right for them. I'm sorry to be blunt, but if your husband allows the kids to be treated poorly by his family, then you have more serious issues to consider than just distance. Since you have family where you are now, I assume they can provide needed support if it comes to that.
All that said, please know that my comments assume your family is kind and welcoming to your husband. If you pray about this and talk to your husband in an open and loving manner, you'll make the decisions that are best for your children and your family. Assuming you and your husband are on the same page regarding the kids and your commitment to your marriage, do your best to make the decision with your husband. The last thing you want/need is for him to blame you in the future if things aren't rosey.
Good luck. I'm sorry you are going through this.