Complex sentence: Starting in the mid- 1970s, Frankie began working with his brother, joining him on the road during Gaye's concert tours and sometimes, to test audience reactions, Marvin would place Frankie onstage first before he arrived.
Split into simpler sentences: Starting in the mid- 1970s, Frankie began working with his brother, joining him on the road during Gaye's concert tours. Sometimes, to test audience reactions, Marvin would place Frankie onstage first before he arrived.