My father, a farmer, has passed away. My parents were married without a prenuptial agreement. My brother is claiming a deferred salary credit against my father’s estate. Will this claim also have to be settled by my mother’s estate?

No. The deferred salary credit is intended to compensate for unpaid assistance provided by a descendant to the farming operator. Since your mother was not herself a farmer, your brother cannot claim a deferred salary credit against her estate. Their matrimonial regime has no impact on this matter.