Is it permissible to sign a waiver of the right to an old rented shop to enable a brother to sublet it, knowing that refusing to do so will cause family problems?

The law of perpetual lease is religiously null and void due to the unknown duration. Therefore, the leased property reverts to its owner, and the lessee must pay the fair market rent for the period of usufruct. The questioner and his siblings have no right to the property, and it is not permissible for them to dispose of it without the owner's consent. It is not permissible for the sister to sign the waiver, as it constitutes aiding in injustice and illicitly consuming wealth. The sister can advise her brother and explain the religious ruling to him.