1. It is not at all ancestral property.Your grandfather was a tenant and on his death his class-I legal heir were being alive whcih included your aunt t inherted the tenancy as well.
2. The same is with his other children who jointly inherited the tenancy except the married daughters.
3.Now when you purchased the proeprty you stepped into the shoes of the original landlord and your aunt became tenants under you.
4. So only way to get the vacant possession of the proeprty is to file a suit for eviction agaisnt your aunts or cousins.
5.Your mother is half owner of the proeprty and hence she can transfer her half share to anyone she chooses. On her death though your aunt will not inherit any sahre from her.