You can apply to the court for a residence order but where your wife agrees to your child coming to stay at your home you don't need a residence order. Nor does your fiancée need a parental rights order. All you would need, if you want it, is a supplementary Minute of Agreement narrating the change of residence for your youngest child. Happy to discuss further. I hope that helps. Please leave a positive rating so that I am credited for my time.