How to avoid adverse possession of land?

Long story short , My great grandmother had some property. She had 5 children. Out of which one of them (my grandmother) took the entire responsibility of taking care of the land by cultivating and growing trees in a well planned manner. She took care of the entire property for about 30 years. And she passed away a couple of years ago. Now she has 4 kids, and the four kids considered the entire property as theirs, and divided the entire plot as they agreed. Now we get a call from my great grandmothers kids asking for a share of the property since on paper the land belongs to my grandmother. How do we solve this issue ? Do they have a right on the property? They are currently asking for either the land or land value as per prevailing market rates.