If both parents have shared custody then its unfair of one parent to move interstate and automatically think they can take the kids. Just as assuming the children will share holidays with one parent. Its not 'shared' then.

If i was to seperate from my DP i would want to stay well away from the courts and work it out ourselves.

It is a very difficult circumstance to be in, and not as clear cut as you seem to think. It is perhaps something you can only understand if you have gone through it yourself.