So split the aunt's property in two and he takes the sheds as part of his inheritance.
May not be that simple for lots of reasons
For a start
first house will need a half acre site,
we don't know where the septic tank is located
we don't know where the water connection is located
we don't know if splitting the property will slow down sale according to op father doesn't like the idea of someone else accessing the sheds it is not just because of the machinery issue he wants to hold on to them,
Buyers may have the same Issues as op father has when the property gets split,
even if they get a sale we don't know what issues crop up at engineering stage,
DR Strangelove posted this is a human problem not a financial problem,
well it appears to be turning into both a human and financial problem,
The op says one of the brothers has no money and is greedy but I don't think from the posting he is greedy more likely he wants his share as soon as possible,
Splitting property may make it unsaleable or at the very least slow down both the selling the closing of the sale ,