If there is no initial agreement and if mediation hasn't resolved the issue, the matter goes to court and a court order is obtained.
The court order deals with
where the child lives
how much time the child spends with each parent
what kind of contact is involved (phone calls etc)
It's called a 'Child Arrangements Order'.
Although I know that you are worried about this, it's better to concentrate on things like your school work and your friends.
This is an aspect of their divorce and, as such, it's something for them to deal with using the support of the courts.
My step mum wants to take my half sisters to another country like very soon, but i don't think that would be healthy for my sisters since she has some issues mentally and by that i mean anger issues ,that need her to take some form of medicine but she doesn't want to because according to her it makes her feel like a ginny pig. I told her the education system here is way better and it will be better for my sisters since they get to see us and she said she doesn't want to see my dad. I'm just worried so i want to know wether she can take my sisters away without talking it out with the father?
From the Gov website - 'If it’s a major decision (for example, one of you wants to move abroad with your children) both parents with responsibility must agree in writing.'