Is it possible that your xh is using the move to LA as a ploy to get you to jump thru hoops to lower the child support payments? Manhattan is an expensive area and so are some parts of LA. I honestly do not buy his sob story of having the relocate because of expenses. He has choices to make and he's made some bad ones. I'm sure if he and his ow looked around, they could find more suitable housing that will more than fit within their budgets. If two people are working, they have to be able to afford something cheaper than where they are.
I have to agree w/kml and Ginger, you can't force him to be a good father and be there for his children. The more you try to fix the situation, the worse it's going to get.
If you are seriously thinking of going thru w/what your father suggested, I hope that you will think about everything. The less money you receive for your children, the less you'll have to give them the things that they need and/or require. Sure, you work and have a good job...but the girls are growing up by leaps and bounds and will require a lot more in the way of funds as they get more involved in activities, etc. If your h truly, and I mean truly, wanted to be father of the year, he would be jumping thru hoops to see his children. Right now, it's all about money I think he's going to try to get the child support lowered and use the threat of moving away to do so.
There is more to this story than meets the eye. If you do go thru w/your father's suggestion, please make sure it is all documented and signed by all parties...but I don't think this is the right thing to do...but that's my personal opinion.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.