Esbee,
I didn't buy my ex out, after months of saying that I would have the house "over his dead body" I got it. too little equity in it to make it worthwhile. Unfortunatley (SP) the sod is still breathing
Get a survey done, and get them to retrospectivley put a value on it at his time of leaving. If it is not totally extreme (the house) ie far more than you require you should be able to keep it (if your dependents are also his depandents)
He has a legal obligtion to ensure his kids have a roof over their heads.
BUT I got divorced in Scotalnd so the rules may be different,
My advice would be FIGHT FIGHT FIGHT. You are in the right, you look after the kids. Also courts up here take into account the emotional stress that the kids would face if you moved.
If your ex is anything like mine it's all talk no action
Get your maintenance agreed by the court and mortgage lenders will then take that into account, also take WFTC into account (even the childcare aspect).