Structural Engineer

Hi I have a problem with my rear garden out building/porch which sits flush with external brickwork of my house. The structure has moved with a vertical crack about 35mm wide at top. I believe the main back wall of this structure is my boundary wall. My neighbours are council tenants and their garden sits higher than mine, their patio was raised without any retainer or drainage which means I have soil stacked against my building wall and they also removed a tree, this has caused damp. & I also have soil falling through crack. I want to demolish building but need advise as their garden will fall into mine.