My sister's father in law in India had passed away 17years back wherein he had left a will leaving his entire property & savings to his wife and not to his 2 sons & a daughter.Now the wife has passed away 3 months back but prior to that she made a relinquishment deed in regards to the property in favour of the younger son only which was duly registered.Now can his living sister challenge the same in court and demand a share of the property?.Thanks in advance