What is the ruling on allowing one's wife to attend a wedding that includes forbidden things like music, and is the husband sinful for that, and what is the correct Shar'i (Islamic legal) action in such cases, and what are the regulations for attending such events?

It is not permissible to attend a place where evil is committed unless there is a necessity, or if one attends to denounce the evil, in which case attendance is obligatory. The husband must prevent his wife from attending such weddings, and he sins if he does not. If she insists and goes out, she is disobedient (nashiz). Ibn Hajar al-Haytami mentioned in "Tuhfat al-Muhtaj" that attending a banquet where there is evil is not obligatory, but permissible, due due to the ill-opinion that might be held of the invited person if he attends. However, if the evil can be removed by his presence, then he must attend.