Agricultural land Partitioned without the consent of my Father which is a Ancestral Property

Dear Sir/Madam, I have a question regarding the DKT land which is an Ancestral property . 1. My Grand Mother(Father's Mother) is one of the 3 daughters of my Great Grandfather and she was gifted a part of DKT land from my Great Grandfather which is not officially partitioned but she was told and shown a part of land along with other 2 daughters where they have also got 1 part each. Since then my Father who is one of the 3 Son 's of my Grand mother was living separately as he was in Army and later serviced as a security officer in State bank. Now the Issue is the part of the land which was shown and gifted to My Grand Mother was occupied partially 1.15 Acres out of 3.77 Acres by My Grand Mother's Sisters Son's . The issue here is My father was not known that it was partitioned and they have occupied some part of the land which belongs to my Grand mother . Which partitioning the land my father was not available and no intimation given to my Father and no agreement made between my Father and any of his Cousin Brothers. We got to know that one of my Father's Sibling was informed about the partition but there was no action taken or effort made to stop the partition of land which actually a DKT Agricultural Land. My question here is can we file any suit in the name of all the Cousin Brothers who have partitioned the land and also occupied the land without my Father's Consent. Please advice on the possible scenarios to take action on this situation.