How can the magic of separation be undone remotely, given that the wife and children refuse any attempt to undo the magic, and is there a specific way to undo it?

It is recommended to seek refuge in Allah, for He answers the distressed and removes evil. One should not despair of reform and should try to involve wise family members. What happened does not necessarily have to be magic; even if it is strongly suspected, legal Ruqyah is the best means of treatment. It is not permissible to accuse anyone of practicing magic without evidence.