Dual citizen / illegal construction

My neighbours, not mundkar had purchased a part of my plot approx. 165 sq.mts from the land lord. my father inspite of being mundkar purchased the remaining part approx 430 sq mtrs. via sale deed. In the 180 sq mtrs they started with illegal construction not even leaving 20 centimeters set back from my boundary wall, which was a matter of concern in the rains and my boundary wall which inturn have developed cracks. My father complained to the local panchayat and to various departments but no one responded to the complaint. my neighbours went ahead to construct 1 room. My father then filed a suit in the junior division and brought a stay. My neighbours had not included their names in form i and iv but form i and iv is a document required to be submitted to attain NOC from any local body. so they later applied. To which my father objected. Now my father got a proof that my neighbour is also a portuguese citizen at the time of purchase of property and has not obtained permission from FEMA. and has also retained his election card and not surrended it maintaining dual nationality. this was brought to the notice of the mamlatdar. but the mamlatdar dismissed my objections saying that she is not a competent authority and that sale deed is the only document required to include name in form i and iv . now i have appeal to the deputy collector. and waiting for his judgement. Please advise. what should i do, how do i challenge the sale deed?