...we don't know the exact terms of the lease, but it might be possible that Sir Walter has leased the whole estate to the Crofts. The Crofts would then take any income from tenants/profits from the home farms etc in Sir Walter stead. And as they were not as financially challenged or extravagant as Sir Walter I daresay it would support them comfortably enough ;-)

Sir Walter would then be able to live off the substantial rent the Crofts paid him.