On the day of my father’s Yahrzeit can i go to my grandson’s Bar Mitzvah with Music and dance? I see the Rov writes not to a chasuna, Is the chasuna a problem because of the music or for other reasons. And if I would be able to go and dance is this according to all shitas.
A bar mitzva that has music would be like a chasuna, because the music gives joy, therefore a person should not go to a bar mitzva and partake in the dancing when there is music there. However since you are the grandfather, it is permitted, the same way a grandfather may attend the chasuna of his grandchild during aveilus. Therefore, in your instance it is permitted.
Mazal Tov and you should have a lot of nachas from him.