We kinda started discussing Hugo and these two at my intro post but we can continue it here.
Since Hugo and Amber were in the same year I feel like they would know each other reasonably well (or at least of each other). They would have had several classes together and then when Amber became prefect and Head Girl, they would have had many more run ins. He probably doesn't particularly care for Amber (unless she let him get away with everything while at school).
Like Sam said below, Hugo and Dom are cousins and so they would know each other pretty well but you can decide how close they are. Unless she completely bitchy to Hugo, he'd love her, think she has a cool job and doesn't believe she should censor herself.