Is the produce of agricultural land considered unlawful if the father bought it with an interest-bearing bank loan, and are the children consequently considered partakers of usury?

If a portion of the usurious loan remains with your father, it must be repaid, and he must repent and not return to it. Even if none of the principal remains, repentance is still obligatory. As for what is produced from land purchased with a usurious loan, there is no harm in benefiting from it, because after the loan is received, it enters into the possession of the borrower and becomes a debt upon him. However, the borrower incurs sin for engaging in usury.