Possession of Land.

Dear Sir, My dad is 82 years old and has purchased 85.6 sq mt out of 114.7 sq. mt of land which is a registered document and Index II. The 2 separate property cards are issued by the City Survey Office. "A" bearing 29.10 sq mt with original landowner name and "B" bearing 85.6 sq mt with my dad's name. My dad constructed a house on 60 sq mt and the remaining 25.6sq mt was kept vacant for further development. Now the Owner's Grandchildren are claiming possession of the vacant land. And they are forcefully(illegally) trying to take possession of the vacant land by keeping the things in the vacant land. We objected to the same however they are using bad language. They are ready to have a physical fight with us. 1. Property Card "A" still in their Grandfather's name and still unable to transfer in their name. 2. After 30 years, the Grandchildren are claiming vacant land neither their grandfather nor their parents claimed possession of the vacant land. I am seeking advice, looking at my dad's age 82 years old is there any legal or court proceedings wherein we can claim the possession of the vacant land on the fast track? Or can we take police help to claim possession of the vacant land? Thank you for your time and advice.