Sheila's use of informal language positions the Birling siblings as fashionable members of the younger generation who adapt their language to the times
Eric is providing short-term solutions (by asking Eva to marry him and supporting her with stolen money), but he does not see the long-term consequences of his criminal behaviour
Eric deliberately uses the plural personal pronoun 'we' to emphasise that it is not just his mother who is responsible for Eva's death, but all of them
As Eric matures and accepts responsibility for his actions, he becomes receptive to the inspector's message that 'We are members of one body. We are responsible for each other'