If Oliver found it odd that his parents moved into his attic bedroom with him, he didn't say so. Of course Hermione knew that their son was far more aware of what was going on than they realized. As much as they both attempted to shield him from the ugliness of the reality of their world, they were only human. Mistakes were often made. Besides, he was fortunate enough to inherit intelligence from both of his parents. It was only going to be a matter of time before he started putting that insight and deduction to good use.