Land Encroachment Issue.

Hello Sir, I am writing this query to enquire about what steps we should take to prevent my neighbors who actually are my cousins, (my father's elder brother's family) from continuing the encroachment on our land. My family comprising me, my two sisters and my elderly Parents are residing in Nagpur, in our own house which is under my father's name. Unfortunately, we are facing a lot of issues there from my father's brother's family, since they have their building constructed next to our house, and my uncle(Father's brother) had illegally encroached upon a portion of our land and had constructed a drainage system upon our land (admeasuring about 3/30 ft) instead of creating a line with municipality high drain. The drain has been creating a lot of nuisance for us specially in monsoon season because the drain overflow and we had snakes in our house and foul smell come out from there daily. And we are facing several health issues because of that. We were unaware of the fact that this drain had constructed there in our house since this sewage system is constructed at the back side of our house, which is unbuilt, we go to know about this drain three years ago when my father's brother died and they had guests in their house and suddenly the drain got leakage was overflown and dirty sewage water with foul smell came to our house so we searched and got to know that this drain is illegally constructed by our father's brother upon our land, without my father's knowledge and consent/permission. At that time we complaint about it to the family members of our father's brother, and told them to remove it but they just repaired the leakage and didn't bother to remove the sewage system from there. Since then the drain had overflown several times but our uncle's family just repair the leakage and change the drain pipes but didn't remove the drainage system. We are constantly complaining them about the foul smell that come from there and the nuisance we are facing because of it, but they are not ready to remove the drain. Now, they are saying that we can't restrain them from using our land for their drainage system as it has been about twenty years since the drain was constructed. And one more thing they had already encroached 2 ft of our land apart from our 3 ft land on which the drainage system was constructed. That means that they had encroached 5 ft of our land. We all are really worried about this issue as it's bothering us a lot. My father's brother has 3 children, two sons and one daughter who is married and her husband who is involving in this matter a lot, is trying to indirectly threaten us. So, my father doesn't want to lodge a complaint against them because they might take revenge on us. As we are daughters so they are trying to take undue advantage of it and they are trying to oppress us. Sir, what we can do in this regard to prevent the continuing encroachment upon our land..? Any Suggestion in this matter would be of great help.