My uncle is gambling addicted. He sold his share in ancestral property. Now, he is trying to sell his house(property is on his name, bought by his money). Most people are not interested in buying this property due to my aunt resistance. Still, some people are claiming that one can buy this property  without anyone's consent. 

 Can a husband really sell his house without wife's approval?   He was proved mentally ill by indian airforce doctors(while serving in IAF). Can this fact help in the case? 

She has consulted a lawyer. Please aware common people in such cases.

If it is his self acquired property then, he can sell it off without anyone's consent. See what kind of mental issue he has. If he is a lunatic, then sale by a lunatic is void. It can be declared void by a competant court. However, he should be a lunatic and not just having some psychological issue or a mere fact that he is addicted to gambling won't make the sale void.

Thank you for the info. Gambling is illegal  in most states of India.  Unfortunately he never got caught. 

He will very likely lose the monies. He does not support her. Infact she and their sons support him. Most of the times he loses all his pension in gambling. Property prices are very high. She can't afford a new house. 

Then, what are her legal rights?

Gambling may be illegal, but sale of property by a gambler is fully valid.

Her legal rights:-

If your uncle is not supporting his wife and IF SHE IS UNABLE TO MAINTAIN HERSELF FROM HER OWN INCOME THEN, she can seek maintainance from him u/s. 125 crpc. Also if she has no other place of residence, she can try to seek residencial orders from the court and order prohibiting alienation of or disposing off the shared household under the DV Act.