How to complaint aganaist neighbour who is Harrassing

I reside in an apartment at mylapore.Its a small apartment where there are only 6 flats. 4 flats are in the front and they have a separate balcony or Open Terrace.2 Flats with a separate balcony. i reside in the ground floor. The entire upstairs leading to the open terrace is grilled. Free movement to the terrace is restricted. Normally my mother occasionally go to the terrace to dry washed clothes. The lady who is residing in the first floor, shouts and pick up quarrels whenever my mother goes up to the terrace. Besides, brings 10 to 15 persons to my house and creates unnecessary nasty scenes. We are also owners of the flat and the open terrace is common for both. However they dont want to let us use open terrace.whenever we try to use open terrace she creates uneccesary problems as she has got local support in my area. They also have a dog rooming in the stairs.Which also makes it difficult for us to go to terrace. also they have extended their rooms in such a way that we dont even get proper sunlight.My bathroom is always dark and i have use it only with tube lights. please do tell me how to take legal action aganist them and where to complaint aganist them for encroachments. .