[Ger-Poland-Volhynia] Filial Church - Granidub - Alexanderdorf

[Nelson]

Has anyone heard of the Filial Church. I've been told that Adolph Itterman b. July 4, 1887 was confirmed in the Filial Church in Granidub in 1902. He would have been  5 years of age. Could this have been a baptism? What is the Filial Church? 
One of my German Dictionaries says Sister Congregation.
Of what?
Nelson Itterman
Edmonton