tyag patra in this case

I have a small question regarding tyag patra. We have a property that is on my mother-in-law name. Lets suppose she did will and gave full property to my father-in-law.after her death my father in law wants to get married. Second marriage. Now in order to save the property .... my husband is planning and are in talking terms to father-in-law to sign on tyag patra.. Will that document be valid... will property come on my husband's name in this case? Is this that The second lady will have no right on the property at any point of time ??? Now in second case.... suppose my mother on law had no will... in this case property gets divided into 3 shares.... one of my father-in-law, one of my sister-in-law and third part to my husband. Now if my father in law is going for second marriage in this case if he signs on tyag patra... will our property br safe from the second wife and her family members..? Please guide me.. how can we 3 safe our property and not get into any complications after the second marriage of my father - in-law...