Mother's & Daughter's share in the property.

If the property is jointly owned by husband and wife ,then after death of husband what is the share of wife and her two children. here the three members have two groups.one side mother and his unmarried daughter and the other side is son and his family. the question is that mother wants her son to sign the papers so that she can sell the house and can buy two flats means one for herself and daughter and another for son and his family.

Mother and son relations are not good and trustworthy and the son is a innocent type of person. now the son doubts that if he signs the paper, he will have no share in his property and how can he trust that his mother will buy another flat. Is there any legal precaution for son that while signing the papers ,her mother should sign another paper to promise him to buy another flat for her son.and if she breaks her promise then what should be done by son to get his share.

Sir total story behind this query is very miserable. So kindly take attention for the son,s rights who is very innocent one more thing that mother and father were govt servants and mother is getting pension and also she received handsome amount after the demise of her husband,.her daughter knows and handles all about the financial structure but the son does not know.