Q [21]  I want to ask that as a Shia am I allowed to offer prayer behind those who does not believe in the imamate of the Ahlul-Bayt?

It is permissible to do so if such prayers cause closeness between the hearts. It is not permissible if this was for the sake of adulation. However, one should recite himself in the first two Raka’ats.

Q [22]  If the imam does not possess a body part or it has been cut off, is it permissible to offer prayers behind him?

It is permissible to pray behind him provided that other conditions of the imam of congregational prayer are met.

Q [23]  If the imam of the congregational prayers is in the third or fourth Raka’ah and decided to recite Suratul-Fatihah, do we have to follow him in reciting Suratul-Fatihah, or can we choose to recite Tasbihat?

It is permissible to recite Tasbihaat three times or recite the Al-Fatihah. If the latter is chosen, the Bismillah should be recited silently during the mentioned Rak’ahs.