Telling the truth, of course.
I remembered Patricia Wrede's retelling, where it's sisters, and three (there actually are three sisters mentioned in some variant of the Twa Sisters, though the third has no part), and the middle one notes the chronic dishonesty of the youngest one.
Mine was honest. Not all tropes aim at adding drama to the story. When the drama doesn't fit, there are plenty of tropes that will sooth it away, forgetting realism, before it distracts from the main story. Characters being chronically honest is one of them.