Will and Settlment

Hi, My grandmother had acquired a property X from her mother when my grandmother was 17 years old at the time of 1957.So now she is a absolute owner of the property X and she has given a registered power of attorney to a builder for selling and promoting the Property X into a apartment complex 3 years back.In the power of attorney she has mentioned the builder cannot sell the land share and only after her signature a sale deed can be done for the Property X. Before 5 years she has given a Registered Will for his 4 sons stating that Property X rights only belongs to the 4 sons and nobody apart from them can claim rights to the property.Just 1 year back his 1 of the son (last of the 4 surving sons) died in an road accident.So after his son died my Grandmother gave a settlement deed for all his sons which 2 flats for each sons from the apartment complex built by the developers from Property X. The last son who died in a car accident is survived by his wife and 2 minor kids. Unfortunately my grandmother died 2 weeks back.She was the absolute owner of the Property X and she signed all the UDS document for the builders for the Property X.She has to to sign the last 2 UDS documents for the builder before which she died. My questions are. 1.Who will sign the documents for the Property X for the 2 more UDS documents which needs to be signed for the builder. 2.As per Registred Will the 4 sons can sign after her death. 3.But since the 4th son is expired and who is survived by a wife and 2 sons. What will happen to the rights of the 4th sons. 4.If the rights goes to the 4th expired sons wife Can she act as a gaurdian and sign the Property X. Kindly clarify, RAJESH