Barabanki: Three sisters were killed and their mother injured when a tree fell on their house due to thunderstorm in Tikaitnagar area here, police said on Saturday. The mishap occurred in Ichaulia village last night when a tree fell on a house killing three sisters identified as Mohini (2), Rohini (4) and Soni (10) and injuring their mother Urmila (30), they said. While the sisters died on the spot, Urmila was admitted to the hospital, they said.