Complex sentence: He tries to obtain money from his mother after his great-aunt dies, and his estranged relationship with his mother is revealed, while Mark thrives in her company and is given the job of writing her boyfriend's military biography.
Split into simpler sentences: He tries to obtain money from his mother after his great-aunt dies, which reveal their strained relationship. Mark, however, thrives in her company and is given the job of writing her boyfriend's military biography.