A: Firstly:
Jinn is a kind of Allah's creatures which is mentioned in the Qur'an and Sunnah (whatever is reported from the Prophet). They will be held accountable for their actions on the Day of Judgment. Believers among them will enter Jannah (Paradise), and those who are Kafirs (disbelievers) will enter the Hellfire. It is true that humans may be possessed by jinn. Du`a' (supplication) and reciting Ayahs (Qur'anic verses) over the person possessed by jinn are permissible.
Secondly:
Chanting incantations on the wedding night or upon conclusion of the marriage contract in order to prevent the bridegroom (Part No. 1; Page No. 283) from being able to have intercourse with his wife is a kind of prohibited magic. Islam has prohibited this kind of magic and has prescribed the death penalty for anyone who practices it.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.