I'm no expert and would strongly suggest seeking legal advice. However, I am separated and my children live with my partner. My partner has a residency order for the children but this also means that neither of us can take the children out of the country (even for holidays) without permission from the courts. Seek legal advice and good luck!
A friend of mine had legal advice on this issue a couple of years ago and was told that a parent needs to have permission to take a child to live abroad. They can move away but not abroad, and abroad includes Scotland, if they are in England or Wales currently.