The Twelve Brothers
It is Aarne-Thompson type 451, the brothers who were turned into birds. Other variants of the Aarne-Thompson type include The Six Swans, The Twelve Wild Ducks, Udea and her Seven Brothers, The Wild Swans, The Seven Ravens, and The Magic Swan Geese.
A king wants to kill his twelve sons, so that if his thirteenth child would be a girl, she alone can inherit his kingdom. The Queen tells this to their youngest son, Benjamin, and that she will give them a warning with a flag.
After twelve days of waiting in the forest, the sons see a red flag, indicating that they shall be sentenced to death. The brothers swear bloody revenge on every girl and move to an enchanted cottage deep in the forest, where they must feed on animals.
Ten years later, after hearing of their existence, the sister finds them there, where the queen hid them for precaution. Together, the siblings live in harmony. But as the sister rips out twelve white lilies out of ignorance, her brothers turn to ravens and fly away. At the behest of an old woman, she decides not to speak and not to laugh for seven years, in order to save her brothers.
A hunting king finds her and marries her. His mother however, slanders the girl's silence, and convinces the king to burn her. The rescued brothers save her from the flames, and with the mother-in-law executed, all live happily together.