succession certificate - West Bengal

Respected Sir / Madam, Myself Hrishikesh Chakraborty, residing in Kolkata, West Bengal. I want to purchase a 17 years old Flat. The flat is in the name of Mr. Ranjit, however he died 4 years back. Mr. Ranjit have 1 wife and 2 children and they are agree to signature the selling agreement during registration all together, i.e. Wife of Mr. Ranjit and his children willing to sell the property to me jointly. The municipality TAX for that propriety paid till 2016, however mutation not done yet. Even they have not collected any succession certificate related to this property. Now my questions are – 1. Can I able to purchase this property from them, if they are willing to Sign the agreement altogether. 2. Can they able to sell the property without any Succession Certificate, and after purchasing the property will be there any issue for doing mutation. 3. Do I need to perform any further legal process – prior to purchase for that property 4. Is there any further legal process need to be done by the wife of Mr. Ranjit and his children – prior to sell of that property. Your response will be very much helpful for me. Please suggest. You can advice me in my email ID - Thanking you Hrishikesh Chakraborty Kolkata, West Bengal. +91 9007178815.