Ancestral property rights/dispute

Background: My grandfather was adopted by some relative in village. My great grandfather had lot of farming land, some gold and money. My grandfather had 3 children (2 son, 1 daughter). My father was in army so he couldn't stay in village. My father younger brother didn’t study well and start doing farming on that land. Till 14 year of army service my father has taken care of every expense (digging well, building house, medical, brother and sister marriage..etc). On some issue they decided to part away. Property got divided (without paper work, as great grandfather was alive and property was not transferred to grandfather) in 4 parts (2brother, grandmother, grandfather). Since father was in army he couldn’t farm so younger brother keeping farming till father got retired (25 year of service). 3-4 years back my great grandfather expired, before dying he gave 4-5 lakh rupee, gold, silver and many other thing to the my father’s younger brother wife, son and daughter. We had no objection on that as we just financially supported and we wear not physically present during my father job time. Problem: inherently my grandfather got all land on his name. Now my father want to return to village and do farming on his share of land. But now grandfather and younger brother not allowing to do so. As every expense of family for all 25 odd year is taken by my father only now when time came for land, my father feel cheated. Now we are looking for any legal option. Any advice?