For a trouble-free and highly performant zigbee mesh, I recommend getting two of this two-pack of the Sonoff dongle (so 4 dongles in total):
https://www.amazon.com/SONOFF-Gateway-Universal-Assistant-Wireless/dp/B0BFHBPW4C/
This will give you 4 very strong repeaters to place within the church. They can be plugged into the AmazonBasics power supply linked to below:
https://www.amazon.com/dp/B0773JFWDC/
The dongles can be flashed using directions posted by @danabw in the thread linked below:
Pair two of the dongles to each C-8. Place the dongles about 15-20 feet away from each C-8 and in opposite directions.