As a beneficiary of a trust, can you be forced to return money if it was misdistributed & 120 days have passed?

My father left several properties to his grand children. After he passed the properties were sold and funds divided equally amongst his children for his grandchildren. Each child received a copy of the trust and signed a sales agreement that stated the percentage they would receive. Now six months later, my brother is claiming his share should have been more as it was to be divided equally amongst the grand children, not the children, and he has more kids. Can we be forced to return the money to have it redistributed? The trust was created in California.