All perfect praise be to Allah, The Lord of The Worlds; and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
A lease isn`t terminated by the death of the lessor because it is a contract whereby a certain benefit is possessed; therefore, that benefit continues until the expiry of that contract. Afterwards, the heirs may renew it or not. "The lease isn`t terminated by the death of one of the contracting parties if the leased item remained; therefore, we rule that it doesn`t get terminated by the death of the lessor or the leasee." {Nihayat Al-Mattlab/(8/89)}.
If the contract period ended, the heirs may renew it and take the rent, or buy the shops from the leasee, as stated in the book {Hashyat Al-Jamal}, "If the lease period for a premises or a cultivation has ended and the tenant didn`t choose to demolish the premises or take out the plants, then the choice is the lessor`s."
Therefore, in principle, your contract with your mother should continue until its period expires. Afterwards, the heirs either renew the land`s lease with you, then you have the right to lease the shops against a rent, or the they may buy them from you. However, if the lease had no specific period, then it is void and the heirs may take it from you. And Allah knows best.