Unfortunately you are only able to ask one question so I have focussed on the setting of the story and its influence on T. Clearly, one of the reasons why Greene wrote this story was to focus on the physical debris that followed the II World War, especially after the Blitzing in London. More troubling than this physical destruction, though, was what many people saw as the moral destruction of society and the collapse of hope, especially among gangs of young people who had never known a reality other than war and its aftermath.
One of the interesting aspects of the story is that it all occurs in quite a small part of London. The story describes this location as follows:
The gang met every morning in an impromptu car-park, the site of the last bomb of the first blitz... On one side of the car-park leaned the first occupied house, number 3, of the shattered Northwood Terrace - literally leaned, for it had suffered from the blast of the bomb and the side walls were supported on wooden struts. A smaller bomb and some incendiaries had fallen beyond, so that the house stuck up like a jagged tooth and carried on the further wall relics of its neighbour, a dado, the remains of a fireplace.
Clearly where the gang live and breathe and plan all of their stunts is in a place of desolation. Yet it is also evident that this upbringing in rubble has had a profound and somewhat disturbing effect on Trevor. Consider how, when he is trying to get the gang to destroy Old Misery's house, T.'s eyes are described as follows:
T. raised his eyes, as grey and disturbed as the drab August day.
This clearly indicates that at some psychological level, T. is a very disturbed individual, as indicated by his mindless pursuit of destruction. Note too the incident when T. saves the savings of Mr. Thomas for him and Blackie as "a celebration." They burn them together, and T. says something that is intensely revealing:
The last burning note illuminated his brooding face. "All this hate and love," he said, "it's soft, it's hooey. There's only things, Blackie," and he looked round the room crowded with unfamiliar shadows of half things, broken things, former things.
T. clearly shows here that he is emotionally detached or even estranged from normal human emotions, and his intense nihilism finds its most powerful expression in burning the money rather than stealing it.
Therefore the setting has had an incredibly profound effect in shaping T. and his disturbed life, as Greene focuses on one such individual who has been born and raised in an atmosphere of war and has known nothing else.