Do the siblings have the right to claim their share of the money that was paid to the female tenant—their sister—in exchange for her relinquishing the old rental apartment she used to live in, especially after the death of all parties mentioned in the original contract?

The old lease contract, which has no specified duration and is perpetually ongoing, is null and void. The tenant must hand over the apartment to its owner upon request, and it is not permissible for the tenant to take any financial compensation (key money). All their earnings and benefits from it are unlawful and ill-gotten gains. Therefore, the brothers have no right to demand a share of the amount paid by the apartment owner, and the sister must return the amount and ask for forgiveness.