Complex sentence: Baba Yaga rebukes him and sends him to her sister; there he fails again, but he is sent to the third sister, where he catches her but no transformations can break her free again.
Split into simpler sentences: Baba Yaga rebukes him and sends him to her sister, where he fails again. However, when he is sent to the third sister, he catches her and no transformations can break her free again.