Kernrechtsfrage
Whether the lease was validly transferred from the heirs to the mother alone without written form
Extrahierter Entscheid
The lease relationship inherited by the heirs was later modified by conclusive conduct so that the sons exited the contract and the mother remained sole tenant; no written form was required.
Extrahierte Begründung
A lease modification is generally subject to no form unless the law expressly requires one. The heirs’ long-term conduct, the landlord’s treatment of the mother as sole tenant, and the sons’ silence justified finding a tacit contractual transfer/renunciation.