Complex sentence: They both worked hard for everything they achieved and are determined to instill a solid work ethic in their children; they agreed to pay for one riding lesson a week, but also insisted that Stevie work at the barn in exchange for additional lessons.
Split into simpler sentences: They both worked hard for everything they achieved and are determined to instill a solid work ethic in their children. They have agreed to pay for one riding lesson a week, but Stevie must work at the barn in exchange for additional lessons.