Will a person be liable to pay rent on behalf of his brother

One thing you did not say that, whether there is any written Tenancey Agreement in between the Land lord/ Flat owner and your father or not. Secondly, from the Tenant Side whether both your father and your uncle sign on it as Tenant or not?
If your father and uncle jointly make Tenancy Agreement with the Flat Owner. Then without doing something, please cheak that your uncle paying rent through Rent Controller under which status. If there he showing single tenant, then your answer towards is very much clear. And on the other hand, if he shows co-tenant, and deposit rent for only his share or 50% share, then the procedure to handel the landlord will be different. Please clarify it first.

Your query is totally contradictory , as what I have understand from the same please note that landlord notice is bad in law, as he has no right to seek enhanced rent from 1984 . Checkout first how long your uncle deposited the amount with rent control and during the period whether the landlord issued any notice or not.