he is soon going to be the main financial provider not just for him but also for his parents and now Helen and Henry.

Tony & Pat could sell the farm & associated businesses and retire on the money. Tom is not doing them any
favours in taking it on, they would probably do
him a favour by giving him terms that no bank would contemplate. And it should be a transaction that is beneficial to parents and
all their children. It has been a storyline before and, no doubt, will be again in the future.
Not quite sure why Tom is supposed to be a provider for his sister and offspring. Does your brother provide for you?