That is completely insane then. They have no Biblical authority to place another man in authority over your wife. Nor do they have any secular legal authority. They sound drunk on imagined power.
The key thing here is to work out how to get Grace also to reject this attempt by them to control her behaviour. You can reject it, but you've got problems with her submission to you. But if she could understand that this is illegitimate power-hungry nonsense, and the two of you really do need to work out your problems yourselves not be ordered around by others who imagine themselves to be in authority over you, that would be a major step towards functioning as a team.
The key thing here is to work out how to get Grace also to reject this attempt by them to control her behaviour. You can reject it, but you've got problems with her submission to you. But if she could understand that this is illegitimate power-hungry nonsense, and the two of you really do need to work out your problems yourselves not be ordered around by others who imagine themselves to be in authority over you, that would be a major step towards functioning as a team.