We to will be in the same position as you, we want to take my son from previous marriage who is 11 and his 15 year old sister (daughter) to Australia, after going to court 4 years ago for custody over the children, my son now sees his father twice a month and my daughter does not see him at all after his current girlfriend banned her from the house for not wanting to spend Christmas with them 3 years ago.
Anyway, even after the court issued an order for the care of the children, their father does not follow this and chooses to have his son in the holidays when he wants and not what is stated in the court order. I am prepared to take my ex to court if he refuses to let my son move to Australia, they rarely see his side of the family so I cant see that being an issue.
I hope like amber2106 ex that he signs the papers and lets him go. This move is for my children to better themselves and become who they are meant to be.