Format of NOC from sister giving up her claim on propery

Sir/Madam My parents in law have two children,my husband and his elder sister who is married to a senior Govt official and is quite well off.In the name of property they( my in laws) have 2 apartments and a small plot of land. While my in laws want my husband to solely inherit their property (they have expressed this desire orally to my husband),I believe that things should be documented.While it will be rude and awkward to ask them to prepare a will right now as they are both very active physically,we can request them to get an NOC from their daughter giving up her claim on the property.However I am not aware of the procedure of getting /format of the NOC.I belive that my sister in law is for sure going to create problems for us in the future if all the documents are not in place.She,being a homemaker and a below average student has always been absolutely jealous of my academic achievements and career despite the fact that she is leading a much more secure and lavish life and is also much older to me.Kindly help me on this.Thank you.