Jesus continues to use fruit trees as a metaphor to refer to false prophets. Here, he only states what will happen to the bad trees. It is implied that the same thing will happen to the false prophets. (See: [[rc://en/ta/man/translate/figs-metaphor]], [[rc://en/ta/man/translate/figs-explicit]])
The word "their" can refer to either the prophets or the trees. This metaphor implies that the fruit of trees and the deeds of prophets both reveal whether they are good or bad. If possible, translate this in a way to refer to either one.