What is the ruling on attending a wedding party where there is doubt about the use of an organ therein? And what is the ruling if the hosts of the party become angry due to my absence?

It is obligatory to accept the invitation to a wedding feast if it is from the husband, but it is disliked if it is from the wife. One should not fail to attend unless there is a strong presumption of the presence of a forbidden act. However, if there is doubt, one should attend. If you find a forbidden act, you should denounce it. If your denouncement is not accepted, then leave. If you are unable to leave, there is no sin upon you, provided that you denounce it in your heart and do not listen to what is forbidden. Attendance is obligatory, whether the inviter is a man or a woman, if it is the husband's feast, with the aforementioned condition. It is good to advise them to abandon musical instruments.