Is the money earned by a young man who works in transporting workers and flowers, and overseeing their arrangement and coordination at weddings, which often take place inside churches, lawful or unlawful?

The money your fiancé earns from transporting workers and flowers to wedding venues, some of which are in non-Muslim houses of worship, depends on a detailed ruling: What he earns from assisting those who commit forbidden acts, such as transporting workers for service and supervising them in a church, is unlawful (haram). What he earns from other activities that do not involve any prohibition or assistance in forbidden acts is permissible (mubah). Based on this, his money is mixed.