The proximity to churches + lack of ventilation makes this theory unlikely in my head. I also feel that some families would have grabbed some food or water before heading down there.
Presumably it's not meant for the entire town. Just the people who are already in town nearby who have enough advance warning. It makes sense to be in a church since that's in the center of town and you can lock the doors to give enough time for people to get into it and cover the entrance.
If your family were at home in the nearby countryside they'd flee into the forest or something instead.
