Christine, this is tough all the way around--for all of you. I think I appreciate the fact that you said that the mom and dad are BOTH good parents. And, although it is shocking & difficult right now, they can both still be good parents.
Maybe the distance won't last too long--you never know--maybe the mom will go to Virginia and soon the new husband will realize the sacrifice he's asking her to make and maybe he will begin a search for new employment closer to the children.
Until then--I agree with Frank--hang in there and be as supportive as you can. And focus on the importance of the role you now play in the lives of your husband's children. And to your husband.
Good Luck!