Should a grandfather who favors some of his children in giving gifts be informed about the Prophet’s (PBUH) emphasis on justice among children, even if this would anger him, or should he be left as he is?

Praise your Lord for enabling you to reconcile with your grandfather. Honoring a grandfather is as obligatory as honoring a father, according to scholars. As for advising him against unequal distribution in gifts among children, this is a debated issue. The majority view is that equal distribution is recommended, not obligatory. However, those who consider it obligatory permit unequal distribution when there are justifiable considerations. If your grandfather favors some of his children without a legitimate Shariah justification, and advising him would anger him, then it is better to forgo that and instead use righteous and good people as intermediaries to explain the Shariah ruling to him.