Writing these dynamics requires nuance to avoid slipping into cheap melodrama.

Never have a character say, "You never listen to me!" Show them trying to speak over three different conversations while the family ignores them. Action over exposition.

Every family has an Original Wound—a death, a bankruptcy, an affair, a move across the country when a child was 11. This event froze everyone into a role. Identify the wound. The entire plot is the family's attempt to either heal it or rebury it.

The horror isn't the ghost; the horror is the mother who joins the cult that possesses her son. Here, family loyalty literally becomes a curse.