Sounds like you are saying everyone in yours and your ex spouse's family lives in the other state where you want to move, but that your ex spouse with whom you share custody, lives here. If that's the case, if your spouse will not voluntarily consent to the move, then you will need a court order. Whenever a parent requests a move-away order, the court orders a custody evaluation at yours and your ex's expense. In terms of your chances; no one can predict that for and it would be entirely inappropriate for someone to try. I would highly recommend that if this move away is absolutely necessary, that you obtain legal counsel and not try to get your move away order alone.
If I understand you correctly, you will be moving closer to your ex and therefore the children will also be closer. Why would you need permission from the court to move closer to your ex? The only reason the court needs to be involved is if the other parent objects.
No one can tell you your chances, especially not over the internet without the facts. But you should absolutely talk to your ex about this immediately. If the ex agrees, then you can move. If the ex does not agree, you will need to file a request for a move-away. The process is long, so get started. Good luck.