I can sort of see the Arsula-Rob thing. We know from Rob that he feels very much the second best son, and from what I've seen in family dynamics, that feeling tends to stay with you no matter how old you are. If he and his brother were brought up to compete for Arsula's affections, at the moment Rob must feel he's on to a winner. His mother is there, giving him all her attention, and she's not with Miles. Rob's been conditioned from birth to want to please her, so that's what he does.
In that sort of situation, dismissal of other siblings' feelings can seem entirely normal. They're competition, and if they're seen as bad or incompetent that can only be good.
Rob I think at the moment, if not always, sees Helen in the light of another sibling, and as competition (remember how when A first appeared, she seemed to favour Helen and that Rob didn't like that at all). He has to come first with his mother, and that's what's most important to him. He's still treating Helen in much the same way, but I think the reasons for it have shifted.