Complex sentence: Cynthia's father and mother are killed after being drained of their blood, while Cynthia's sister, Ellen, is fed upon and transformed into a new vampire bride to serve Yorga.
Split into simpler sentences: Cynthia's father and mother are killed outright after being drained of their blood. While Cynhtia's sister, Ellen, likewise is fed upon and transformed into a new vampire-bride to serve Yorga.