Court order as part of divorce?

[Blenkins]

I have 3 dc, one late teens, one mid teens and one late primary. Split from their dad for 7 years. He remains controlling, just as he was during our marriage, but it’s incredibly subtle.

Eldest chose to live with him 3 years ago. Out of the blue, they decided between them without any discussion with me and within a week dc had moved out. Had (and still do) a great relationship with dc1 and so this was an absolute shock and hurt very very much. We had always agreed that the children should be together, wherever they were, so lived with me and went to dads once a week and every other weekend, plus shared in school hols, and this totally went against this agreement.

I think ex had been angling for it for a while and I don’t believe for a minute that it was dc1s idea.

I have a feeling that he is doing the same now with dc3 (dc2 is a trickier character and doesn’t get on as well with their dad so wouldn’t want to go. I don’t think ex would want dc2 to live with him either)

When we finally divorced (took ages) dc3 had already moved but divorce arrangements included that dc2 and 3 lived with me as per arrangements above. Is this a court order? Or would I need to apply for it now?