You used the phrase "apparently legal" and wrote they are burning trash. The state of Florida has regulations on open burning which can be found
HERE.
Included is this regulation:
What materials are prohibited to be open burned in Florida?
Open burning of biological waste, hazardous waste, asbestos-containing materials, mercury-containing devices, pharmaceuticals, tires, rubber material, residual oil, used oil, asphalt, roofing material, tar, treated wood, plastics, garbage, or trash is strictly prohibited.
There is also a pdf of the regulations that can be found
HERE
Burning of allowed material is also controlled with rules about the exact hours it is allowed, the size of the pile being burned, the requirement that fire extinguishing equipment be at the burn site, and that a person must be present while material is burning.
The church may very well be in violation of state regulations if they are doing what you describe.