Bride: The Hunter Book I. The Hunter, #1

After a failed exorcism, a young Priest is assigned to accompany a unique team to deal with a demonic possession involving multiple demons with a plan for taking over the world and ridding it of humanity. It takes a while to determine the precise location and they determine that one of the demons has taken possession of a woman taking part in a lesbian wedding at a nudist resort in South Louisiana.
As the team is investigating, the demon begins preparing others to receive one of the five demons necessary to accomplish her mission. The team, with a little help recruited from within the wedding party, must locate and banish all six demons before the ritual can be completed to open the Gates of Hell.