Illegal land occupation

Dear Sir, I purchased 1.38-acre agricultural land from an old lady(75 yrs). Background of the old lady: She owns 7 acres of agricultural land(6 inherited from husband and 1 earned by herself). She has only one daughter and 4 grand-children(2male, 2 female). She distributed 6 acres to the grandchildren equally and staying with one of the granddaughter keeping one acre for herself. I purchased the share of one of the grand-daughter where the old lady is staying. The land is, first got registered on the name of the grand-daughter and then, I got it registered on my name. Now, one of the grand-son wanted the remaining one acre registered on his name and the old lady stay with him which she refused. In revenge, he illegally occupied the agricultural land with local political support. (His true intention in doing this is, I go back to the old lady for the problem resolution and it forces her to register the remaining one acre to him). During the registration, they have given me the joint declaration paper where everyone agreed for the fair share of the land among themselves, except the remaining one acre and no one interfere with other's land. I could not approach the local police as they bound to political pressure. Could you kindly suggest the best approach I deal with this situation? Regards, Naresh Kavala.