Family dynamics are fluid. Two rival siblings might unite against a parent, only to betray each other when the immediate threat passes.
The antagonist must believe they are protecting the family. A controlling mother should act out of a distorted desire to keep her children safe from the mistakes she made. Family dynamics are fluid
A family built on a lie is a ticking time bomb. The revelation of a hidden truth—such as an unacknowledged sibling, a hidden crime, or a falsified identity—shatters the shared reality of the characters. a hidden crime