Purchase - Deceased Father and released Elder brother property

Hello, I want to purchase a property in Mumbai wherein the property was bought by a Father(F) and Elder son(ES). The name in the original sales deed has F and ES name on it. The original share certificate has also F and ES name of it. They belong to a Muslim family. F has 3 sons - eldest son(ES), Middle son(MS), youngest son(YS) Mother(M) is alive. F is deceased now. YS and M are staying in the property presently. ES has signed a release deed to transfer rights of property to YS and M on a non-judicial notarized stamp paper. The housing society of the property which is 11 years old has transferred the shares to the YS and M on the basis of release deed and application to society of transfer of name.Their names are also added behind the original share certificate by the society. There's another document as Power of Authority signed by ES and MS to transfer rights of property to YS and M. The maintenance receipt has YS and M on it now. ES and MS are living abroad and not present at the property. YS and M have published an advertisement in the local newspapers to declare their rights on the property. They have kept the newspaper ad with them. There is no nomination form available with the society at present. My question is that if I want to go ahead to purchase the property then are the above documents (original sales deed, release deed, power of authority, share certificate with names added, newspaper ad) considered legal proof and okay so that I can transact between YS and M, or is there any document that is missing and I need to request the sellers? Thank you, M