Is there a sin upon the questioner for working in a hotel that hosts wedding parties with music and songs, and where he is assigned to play records, and that accepts guests married by Misyar marriage?

There is no objection to working in the maintenance of hotel halls. However, assigning an audio technician to play singing and music discs involves assisting in a forbidden act, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." If it is possible to refrain from that, then there is no objection. Otherwise, it is not permissible to continue except out of necessity. Misyar marriage is permissible if it fulfills the conditions of a valid marriage.