Podnájemníci (1976)

This is the first part of a loosely connected trilogy following two orphaned siblings: Alenka, thirteen, and Zbyněk, twenty-three. The story centers on their unusual family dynamic, where they've essentially become each other's parents. Zbyněk wants to marry, but Alenka's jealousy prevents him. To resolve this, he brings his girlfriend, Katherine, to live with them as a lodger.