Complex sentence: Her nephew was a classmate and close acquaintance of Tsarnaev at Cambridge Rindge and Latin and along with a group of his fellow classmates, Tsarnaev attended a senior pre-prom party Young hosted.
Split into simpler sentences: Her nephew was a classmate and close acquaintance of Tsarnaev at Cambridge Rindge and Latin. Along with a group of his classmates, Tsarnaev attended a senior pre-prom party Young hosted.