Selling ancestral property

We have a problem in selling our property. My grandparents died and the ancestral property was shared among the grand children. My father is the first son in the family. My father left my mom since 16 years and we were brought up by my maternal uncle from our younger age, I'm his daughter 22 years and I have a brother aged 16 years. We did not asked for any money help from my father's family the only sole they have us is this property. There are talks that my father have an relationship with a lady and also gave birth to a son. But we have never seen him since 16 years. And my mom did divorce my father so he the legal father for us. Now we are trying to sell the ancestral property, and my father's brother is asking a share from us and he is standing obstacle for selling the property. He is saying that my father is struggling a lot without Money and we have give a share for saving his second family which is bloody irritating. My mom struggled a lot to grow us up and he is asking share to a emotion less father who did not even bother to see me and my brother since 16 years but only need money from us. Please advise.