Somebody has to have 2 fences since there is always one more side fence than houses in a line of terraced houses. In my case I am the second last house to the left so my neighbour to the left only has one side fence to maintain. At the other end of the line I assume the end house has two fences...
Yes, that is certainly how mine works. I maintain the fence to the left and my neighbour on the RHS maintains the one to my right as I look down the garden from the back door.