I think the Bates and Dugger families met thru their home school network, and the yearly conferences they attended.
Gil Bates pastors a Baptist church near their home in TN.
I interpreted the shows cancellation to be based more on the fact the show is no longer in line with the original concept, which was to show how parents today are raising a very large family. Once the older Bates children married and started their family, there's less focus on life at home with Gil and Kelly, and more focus on expansion of the adult childrens families.