What is the book series with an evil uncle and three orphaned children claude violet younger sister im not sure?

You're describing the A Series of Unfortunate Events by Lemony Snicket.

* The evil uncle: Count Olaf

* The three orphaned children: Violet Baudelaire, Klaus Baudelaire, and Sunny Baudelaire (her name is confirmed, not just "younger sister").

Let me know if you have any other questions about the books!