Complex sentence: The world of talented painters and sculptors in New York City was small and Mitchell became friends with many of them during this period including Franz Kline, Jasper Johns, and Robert Rauschenberg who both lived above Mitchell's other loft on 128 Front Street in New York.
Split into simpler sentences: The world of talented painters and sculptors in New York City was small and Mitchell became friends with most of them during this period. Johns & Rauschenberg lived above Mitchell's other loft on 128 Front Street in New York.