Prepatual lease after hakshufa

In 1958, my grandfather and his 3 brothers divided their commercial property into 4 parts, with my grandfather receiving 26.5 marlas and registering it in his name through a 'patta dawami'. However, he also gave ownership rights to others through a 'hakshufa'. I would like to know if this arrangement constitutes a 99-year lease or a generational transfer of ownership, and if we can claim ownership from the current holders, given that they acquired it through an illegal sale.