Can an avel be at his daughters wedding that has music, after shiva before shloshim?
Hamakom yinachem eschem btoch shar aveili tzion vyerushlayim.
Regarding your question, the father of the chosson or kallah may attend the wedding even though there will be music there, however he should minimize his dancing. Regarding new clothing, someone else should wear it for half a day of a day before putting them on, and then they can be worn by the avel.
Maharashdam Y:D 202, Melamed L’hoil 143, Shevet Halevi 10-219, Tziunei Halacha pg. 508.