I don't thing any of the characters fully found atonement. The only one that came closest to it was Briony. I think she would have achieved it more if she had told the truth before Cecilia and Robbie died. If she would have said that she knew that she lied about the raping, then perhaps they would have been able to be together. The fact that she wrote the story after the people who were involved had passed away did not fully give her this. Briony constantly mentions and thinks about making amends, but never does. I do not really pity her because she had numerous chances to make things right, and never did. Even when she grew older and knew right from wrong she never did anything about it.
Marshall was the least closest to finding atonement. Right there next to him was Lola. They both knew the truth and did nothing about it. Lola knew who it was who had raped her, and that it had been going on for awhile, but she hid it. Her hiding it is more understandable than Briony, but then she goes on to marry Marshall which is awful.
The parents were even guilty of this lie. Everyone in the story in some way or shape had to know the truth, or at least that Robbie was not the rapist. Robbie comes back with the twins, with no clue about what happened, and they quickly accuse him of it. The parents are listening to the story of a 13 year old girl, who is clearly doubting herself as she testify s, and Lola had bruises on her which no one ever noticed. I find the title of the book ironic since everyone in the story was guilty in some form, and no one finds a way to make things right