This is a self-acquired property and your uncle is the absolute owner. He purchased the property out of his sources. He has an absolute right to transfer it to any person. No person can compel him to alienate the property to a particular person. Your aunt has filed a false case under domestic violence Act only for forcing him to transfer the property to her.
If a person files, a false lawsuit for an ulterior motive, he thereby abuses the process of the court. The High Court has inherent power under section 482 of the code of criminal procedure (crpc) to quash such a false case. Hence, in the current scenario, your uncle should file a petition before the High Court under section 482 for quashing of the domestic violence case.
As far as the police officer is concerned, he has no right to compel a person to execute a Will for the transfer of property. You may file a complaint against the police officer. He may file a complaint before the Superintendent of Police of your district.