If you are crafting a family drama storyline, you need inciting incidents that break the dam of repression. Here are the most effective plot devices.
Family drama works so well because the stakes are inherently high. A stranger betraying you is a tragedy. A sibling betraying you is a wound that never fully heals. This is due to what psychologists call "high emotional valence." We expect the world to be cruel, but we expect our family to be a sanctuary. When the sanctuary becomes the battlefield, the visceral impact on the audience is immediate.