Complex sentence: Shumbh and Nishumbh came to know about Dhumralochan's death and Jagadamba this and sent Chand and Mund to kill Jagadamba and to kidnap Kaushiki.
Split into simpler sentences: Shumbh and Nishumbh came to know about Dhumralochan's death and Jagadamba. After learning this, they sent Chand and Mund to kill Jagadamba and to kidnap Kaushiki.