Is the plaintiff subject to sin or liability, and what should he do about his and his family's free entry to Palm Jumeirah by agreement with a stranger?

What you have done by colluding with the man in deception and lying is impermissible, for the Prophet, peace and blessings be upon him, said: "Whoever cheats us is not of us," and "Whoever cheats is not of me." Therefore, seek Allah's forgiveness and repent to Him, and you must pay the price of the island entry tickets to the responsible authority.