It appears as if you varied the hypothetical from the one presented in the other thread you started.
See What are the tax implications of a sibling buyout… (intuit.com)
Is your brother (Peter) no longer receiving $100,000 from you for his share and gifting you the rest?
Note that in a sale to an unrelated third party, Peter's gain would be the difference between the sales price (less selling expenses) and his basis, the latter of which appears to be $155,000.
If, sometime later, Peter wants to then give you $50,000 of the proceeds he receives from the sale, that would be a separate transaction which would require him to file a gift tax return (Form 709).
