The transaction (the so-called bond of release) had been void. Admittedly, your father was alive when the deal took place and the land belonged to your father. Your brother had no right or share in the property which he could have relinquished or sold; all that he had was a prospective right to inherit or succeed in the intestate property of the father. Obviously such a right could not have formed the subject matter of a conveyance, in whichever form.
Now, consequent to the death of your father, the property is jointly vested with the children and the mother. The settlement deed need to be executed by all of them, including the elder brother. Propriety and morality requires that he should honour the earlier transaction and relinquish his share in your favour.
However, there are situations where law cannot enforce the requirement of morality. Unfortunately, to my knowledge, the instant issue falls in this category.
All that could be suggested is an amicable settlement.