In about fifteen seconds of yelling and begging from the two main characters of this drama, it became clear to Eoin that he did not understand a single word that was being said, or at least that there was some context to this whole situation that he was missing and it made him very uncomfortable.
This was what he understood: The man on the floor was Diana's brother, who presumably occupied a higher station in life than she did. Or at least, he proved that Diana hadn't always been the sort of girl who would have been a prostitute no matter what she did, just based on her circumstances. In fact, she was probably a Pureblood (by family, not status) so this whole setup with the broken-down flat and the prostitution was probably caused by something she'd done against the regime.
Suddenly, Eoin was aware that he was in more danger than he'd ever considered. Not that this really bothered him now, but he wondered how thin the ice underneath Diana was, if she'd managed to bargain her way out of Azkaban (he guessed) but only ended up a prostitute. If her brother would talk to her, much less offer to be her guardian, how bad were her crimes, really? But whatever her legal status, it was clear she came from a lot of personal trouble, if the sight of her brother, not to mention how he'd brought up whatever horrible thing her father had done to her, made her this angry.