Do the brothers have the right to claim their inheritance in agricultural land that their mother sold to the questioner before her death with their knowledge, and should the price of the claim be based on the price at the time of sale or the current price?

If the mother permitted her son to sell her land and take its price without an explicit gift, then this price is considered a debt upon him that must be repaid to the heirs for lawful distribution. The debt is repaid with the same amount that was taken, unless its value has significantly decreased, in which case it is repaid with the value of the currency rather than its equivalent. This also applies if the currency itself is no longer in circulation, in which case it is repaid with its value.