How to prevent mentally ill father from selling property

I am a married hindu 40 years old my mother has a property in his name i am the only child i livewith my parents in same roof my father is a quite quarrelsome person with every member of family even with my mother my mother is mentally ill and i take care of my motheafor last 20 years my father wants to sell this property but we dont want to sell it how i can we stop him.my father is a pacemaker patient with oral cancer operated 4 years back and he is normal now.