Well nobody trashed the Victron dealer who told me the AutoTransformer (placed in Location A) would solve the problem of powering the GSHP and providing 120V to the cabin. So it seems that this should work.
Thank you fellas for digging into that. @Hedges do you agree the most that GSHP will demand is 4600W which is no issue for the Multiplus supplying 8KW?
He will once he sees RLA and LRA are the same.