unauthorised construction of steps in common passage

Sir, I reside in a muncipal town named Gudivada in Andhra pradesh. My mother purchased a plot of 150yards some 30 years ago and we constructed a house some 25 years ago. Actually the said site was divided into three plots ours is last one from the muncipal road. That means we have to go through a common passage( arranged by the site owner at the time of purchase and the same is incorporated in our documents) to reach our house by crossing the first plot owner and second plot owner. The main owner of the said site has allocated 2 yards way/passage to reach the muncipal road and given common right to the three plot owners to walk and reach the road. That arrangement was incorporated in our registered documents. The said passage / road is in north side to these 3 plots. The first plot owner who faces muncipal road is not walking and he just kept a door in north side for vastu purpose. Now the 2nd plot owner constructs a house in his plot and planning to construct steps out side his boundary wall by encroaching the common narrow passage that is 2 yards. Then the said common passage will become too narrow, even it is very difficult to go by cycle to reach our house from muncipal road if the said steps are constructed. My point of view is the said passage/way provided by the original owner is just for walking but not for any constructions. In this connection kindly ad vise me can we raise objections on the proposed steps which the 2nd plot owner planning to construct. To whom we have to contact for getting justice in this regard whether the town planning officer or an advocate or policemen. Your prompt piece of advice will be highly solicited and we being employees cannot involve in physical quarrel with the 2nd plot owner who is a tough and rough person. We want to proceed legally. Kindly advise us Thanking you, Yours faithfully B.R.K.Rao