How was the property transferred to you by your grandfather at that time?
If it was not by a registered document then whether there was at least any oral partition done by your grandfather or his sons after the death of your grandfather?
Whether your grandfather left behind any Will bequeathing the property to your names?
If none of the above exists, and if your grandfather was reported to have died intestate, then the other sons of your grandfather are also entitled to a legitimate share in the property left behind by yor grandfather.
You first ascertain the situation, consult a local lawyer based on the prevailing situation and relevant facts.
Look for the possibilities for an amicable settlement or partition so that this can be solved even without approaching court for a stretched legal battle.
If there is no other alternative then you may look for the legal solutions to this situation.