What is the ruling on attending a wedding where there is an organ, along with my hearing songs, and does the obligation to accept the invitation cease to apply to me, and should I obey my mother who wishes for me to go with her to that wedding, and are songs unanimously prohibited, and are they major or minor sins?

The prohibition of listening to musical instruments (ma'azif) is a matter upon which the Salaf (pious predecessors) have reached a consensus, and any differing opinion is aberrant and not to be relied upon. Listening to musical instruments is not a major sin unless one persists in it. The presence of a reprehensible act (munkar) at a wedding feast nullifies the obligation to attend if the invited person is unable to change the reprehensible act. It is not permissible to obey one's mother in attending a ceremony that includes a reprehensible act that cannot be changed. Therefore, it is obligatory to repent from listening to musical instruments and to advise those who commit such acts.