Reciting Al-Fatihah by the listeners after invoking Allah, reciting the Qur'an or as a betrothal ceremony is a Bid`ah (innovation in religion). None of these deeds is authentically reported from the Prophet (peace be upon him) or any of his Sahabah (Companions) (may Allah be pleased with them). In fact, it is authentically reported that the Prophet (peace be upon him) said,
Whoever does any act for which there is no sanction on our part, will have it rejected.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.