Of course it is very hurtful but you will have to accept it.
In your place I would drop your parents a letter, advising them to get legal advice as there are pitfalls including future homelessness, if things go wrong for them.
Keep a copy of it.
Giving everything to the favoured son is a very familiar story that I have come across over the years, be it the farm or a valuable house on a large plot.
It has NEVER ended well for the parents.
Their daughters stepped away and there was huge bad feeling.
In one case the son sold up after years of free childcare and moved far away.
His sisters never forgave their parents and have remained estranged to this day.
The other case that comes to mind was a sister who was promised a site on the farm her brother was gifted in its entirety, only to be asked for money for it.
She moved 30 minutes away and her parents were deprived of any meaningful involvement in their ONLY grandchildrens lives.
It is about so much more than money, it is about fairness.
I find posters calling the OP's in this situation grabby, extremely obtuse.
To effectively be disinherited by your parents, in favour of a sibling is painful, irrespective of the amount involved.
Your parents are likely to deeply regret their trusting your brother to do the right thing long term.