Short answer: No. Sideshow Bob (Robert Underdunk Terwilliger) is not the brother of Krusty the Clown (Herschel Shmoikel Pinchas Yerucham Krustofsky).
This is a common point of confusion among The Simpsons fans, likely because both characters have worked together closely in a professional capacity and share a similar exaggerated stage presence. However, their actual relationship is very different. Sideshow Bob was originally Krusty’s long-suffering, classically trained sidekick on The Krusty the Clown Show . Bob would perform Shakespearian soliloquies while Krusty honked a horn and threw pies. Bob’s role was the silent, dignified straight man to Krusty’s chaotic buffoonery. is sideshow bob krusty's brother
Sideshow Bob is not Krusty’s brother. He is Krusty’s former sidekick and a recurring villain. Bob’s actual brother is the equally nefarious Cecil Terwilliger. Short answer: No