Aveilus for a parent and attendance at a grandson’s bar mitzvah. What is permitted?
If the bar mitzvah boy will say a dvar torah, or if it is the actual day that he becomes bar mitzvah, it is controversial, but one can be lenient. It would be better if the avel can do some serving at the bar mitzvah.
If there is music there it is more of an issue, so he should do something to show that he isn’t taking part in the music. For example, learn a sefer, or be busy with something else at that time.
Dagol M’rivava Y:D 391-2, Shut Tuv Taam V’daas third edition 2-86, Divrei Sofrim 391-73 (end – regarding a bris), R’ Y. Cahen shlit”a.