Well, damn, this will put Calvert in a spot, which honestly doesn't bother me, but it will put Granger in one as well, and that does. I am not sure that Granger making this a to do in the House of Lords would be the right thing either, but he will have to have an external pressure that can be brought to bear on the Admiralty to budge them at all.
Having the support of the Granger family has been a help to more than one person; but as Granger said, you also inherit their enemies. How much of an enemy are the Chalmers family; they obviously have a reason, that they believe in, but do they have enough support in the navy or elsewhere to really make anything stick? Is there a Chalmers that is higher than Granger; and still serving? Plus, you would think they would not want what happened in the past to be brought back up either. If I remember correctly, Midshipman Chalmers was so unpopular that not one person spoke up for him asking for mercy.
Granger will do what he has to do in order to help Calvert; but how much of his precious time, energy, and favors will it take to see results. A most devilish issue you have deduced @Mark Arbour