Property dispute

MR X died thus his wife A and children B,C,D inherited his property and sold property 1 and 2 in 1986 and 1989 by way of Gpa collectively to MRS Y.This Gpa was notarised but NOT registered. In 1990 MRS Y built a house on property 1&2 combined and has paid towards bbmp and bescom. They have paid all taxes and power bills till date. In 2010, MRS Y had transferred both properties and house to her son by way of SALE DEED and paid the necessary stamp duty. It's a B KHATA PROPERTY.KHATA TRANSFERS WERE ALSO MADE CORRECTLY. FURTHER INFO TO GET A CLARITY ON GPA EXECUTORS; B got married has no children but died during 90s. C died AFTER registration through sale deed (2010) and D is still alive,is married and has sons n daughters. So since A was the wife ; 1)who has rights in terms of her share? 2)Do B's wife have a right?? 3)Do C or his own family have any rights?? 4)Do D or his own family have any rights ?? 5)Should I get a sale deed from these Gpa executors?? 6)Or taking their signatures as witnesses would be enough ?? 7)Pls advice on who has rights to what extent?? 8)Today, in 2015 can I buy this property?? 9)MRS Y and her son holding the property for about 25-30 years becomes a factor in case of disputes?? 10)Is it advisable to buy the property. If so or not?? Please advice as soon as possible. THANK YOU.