Peace Needed, Help!

My twins are preteens and Cory is 4 so, how can I get my twins to stop teasing and picking on Cory and vise versa?

4Ronna JonesFort Worth, Texas
About Ronna Jones
Born: San Antonio, Texas
Current: Fort Worth, Texas
Birth: December 24
On since: Nov 6, 2013
I am a stay at home Mom of 3 handsome boys and 1 beautiful baby girl. We are now done having children. I Love being a Mom and a Wife. I have been married since June 20th 1999.