“The entire kehila needs to make a taanis if chas v’shalom such a thing happens“
not exactly the entire kehilla. anyone who was present.
it’s 40 separate days of fasting (not nights)
“…..who physically cannot fast, should give a notable amount of Tzedaka instead.”
not physically able is not a necessary condition, the Rabonim allow us in this weak generation to substitute Tzedekah in its place