Hazrat Masruq narrates that Hazrat Ibn Masud (may Allah be pleased with him) would not give the grandfather more than one-sixth of the wealth in the presence of brothers. He says that I told him that I had seen Hazrat Umar (may Allah be pleased with him) giving one-third of the wealth to the grandfather in the presence of brothers, so he (Ibn Masud) started giving one-third of the wealth (to the grandfather).