What is the ruling on performing supererogatory prayers in the mosque at the time of the Iqamah for the obligatory prayer?

As the village Imam, determining the time for the iqamah (call to commence prayer) is your responsibility, and you must consider the benefit of the congregants without causing them undue hardship. If the prayer time arrives and some worshippers are engaged in supererogatory (nafila) prayers, the view of the majority of scholars is that a person praying a nafila should not interrupt it unless there is a fear of missing the congregational prayer, based on the Almighty’s saying: "And do not invalidate your deeds." If there is a fear of missing the congregational prayer, then he must interrupt it. The hadith "There is no prayer except the prescribed prayer" is interpreted to mean not beginning a supererogatory prayer when the iqamah for the prescribed prayer has been called. There is no blame on you for starting the prayer without waiting for them, and if waiting for them does not cause hardship to the congregants, then there is no harm in waiting.