To relocate children abroad consent from all those with PR for the children or permission from the court is required. If your ex won''t consent the court will consider how well though out and practical arrangements are for housing, finances, employment, education and contact.
The primary carer is the parent who primarily is responsible for the children. That isn''t just about the time a parent is actively caring for a child but the times when they are responsible for the child.
The historical living/contact arrangements for the children along with the their relationships with friends and family are important as are the motivations for wanting to move and the other''s parents opposition. For example if there is a poor history of complying with contact orders a court might see a move as purely an attempt to frustrate contact. On the other hand if there has been little involvement by the other parent opposing the move may be seen more as an issue between parents rather than having the best interests of the children at heart.