my son in law died in a car accident recently.my daughter has been disowned by her in laws.we have f

my son in law died in a car accident recently.my daughter has been disowned by her in laws.we have filed a third party claim on the insurance company of the vehicle with whom the accident occured by his fault.kindly advice as to what are the documents required for the case other than the income tax returns of the deseased, and how could we get them ,as my daughter's in laws are not willing to give us the documents. can we get the income tax returns from I.T.deptt.through R.T.I. or the court can give instructions to various deptts.or can order the in laws to produce the required documents,as the mother in law of my daughter is one of the parties in the case.