I agree mi62014. I remember Tessa Shepperson did a little training video on all this. Scenario 1 is not an HMO as they all relate through B. If there were 4 people, where D was partner to C, and C or B left the houseshare, the relationships fall apart and it becomes an HMO. Weird because you would think 4 people is a more risky set up fire-wise than 3 people, but I believe that is the case!