Boundary wall on disputed land

In my Property West side common passage & house of Neighbour A, South side a house of Neighbour B, East pond, North side land of Neighbour A. My dispute is "if I measure from west side both Neighbour come in to my property", "if I measure from south to north side Neighbour B house 2feet 6-7 inches goes inside my house/property & my house/property goes to North Neighbour A property", "if I measure from south to north side Neighbour A property goes 2feet in my house/property & my house/property goes 4feet South Neighbour B house". For Neighbour A boundary wall we could not repair or construction. The house/property is on my mother name, she died 4 months ago. My father is 69+ aged man, he could not move will. I am currently jobless from 3 months & only successor. I have few questions 1) which authority will decide it's a disputed land or property? 2) North Neighbour A build boundary wall 6-7 inches away from my house wall, what should I do? 3) How anybody can build boundary wall in disputed land or property? 4) How to remove/broken disputed boundary wall through legal way? 5) How will local authority help me? Please help ASAP ????