Sounds like he is trying to BULLY you in the hope that you will just believe him. From personal experiences i believe that if he is moving to better his employment that is fine but if he cannot keep up with the current orders put in place they will re look at them and find what is best for the children. You will probably find that the courts will side with the mother as they do in most cases, and they will not change a routine that the children is currently in such as schooling, friends etc.
I have found the courts look down on fathers that apply for full custody, so to be honest let him do it but don't give into him and don't move and continue what you are currently doing with the children and if cannot cope with it the courts will reduce his time to one weekend a fortnight, half school holidays etc
As for not being able to rasie your girls without his help etc what a bunch of b@@@@@@t, you have been doing it to now haven't you. Plus when i was going through all this my XP tried to go down the unfit mother, bad mother and all that crap but he had trouble proving it (because it wasn't true) and to be honest my DH has gone down that street with his XP and she has had DoCs involved and still the child is in the mother's care.
Just try and be strong and don't let him bully you into anything.
GOODLUCK