Common passage drainage issue

Dear sir/madam, In our property agreement from by grand father to my father and uncle (Dad's Bro) there is mentioned that a 4 ft common passage has to be left both from my dad's property and Dad's brother property. Our property is in the front portion, while my dad's bro property is backside of our's. The drainage pipe of our houses flows starts to from property to dadr's bro property to backside and finally to municipality drainage. But since from few days the drainage pipe is getting chocked very frequently near our dad's bro property, we got the suggestion /option leftout to solve the drainage issue permenantly was to replace the pipes as pipes are broken inside obstructing the flow of drainage frequently. But the issue is, the drainage pipe is common passage of dad's bro property and to replace the pipes, we have to remove/break the rock type floor (4 feet length rock stone) to replace the pipes and reset the same. But my dad's bro is not allowing us to do so. kindly suggest....