Purchasing Property from a husband of a deceased wife

I am planning to purchase a house in bangalore, this property belongs to a women who expired last year, Now husband has changed the Katha (tax document in his name) and had paid tax for one financial year. They have 2 son one is 17 years old and the younger is 13 years old. All the documents seems to be fine, He has all the deeds original and the title looks clear and still in wife's name. Now my question is what is the procedure to purchase the property as minor sons also equally inherit in mothers property along with their father. How to purchase this property and what steps to be followed.