So far as his claim that the property does not belong to her since she remarried, it is total nonsense. The plot of land is given to her by her in laws now she has built a three storied structure on it. The structure and land cannot be separate and having allowed to build a house her in laws have given her consent of title to your sister. When he says she does not have any right on the property how can he have any right because he is claiming through her. She can make an application to Tribunal established under Maintenance of Parents and Senior Citizens Act and through her son out to house there is such provision under the said Act.