I am the step-dad going to the military. Dad and mom have joint custody but girl resides with mom. Dad has 2days a week and every other week-end. Will the court allow us to relocate with the child who has her younger sister there with us? Dad does have another son whom the girl sees during those visitations.

If the dad has a visitation order, then mom needs permission of the court to relocate if it will affect dad's exercise of that visitation schedule.

Also be prepared to make consessions like paying for round trip airfares etc for the father to have visitation.

It is very likely that the court will say no, so be prepared for that.

If it does, there will have to be an agreement that the father will accept, and as noted it may mean father will get child for longer periods, "months" and weeks at a time, and that you will have to pay all of the transportation costs for this.

But again the court can also just refuse to allow the child to be moved

It is likely that the answer will be no. Now, of course mom and dad could always try to work things out in the court room where dad gets child for the whole summer and breaks but if dad doesn't want to go for it then chances are the child will not be able to be moved. There is also the issue of the travel expense that would then fall on the mother almost if not entirely.

I want to add, that, if you do not get the permission of the court and you still relocate, you could lose custody or be arrested for parental kidnapping. Or the father can force you to move back. As long as he has court ordered visitation, anything you do that affects that visitation has to go through the courts or the mother will be considered in contempt of court.