AJ and Arlo had a bad relationship in the beginning of the book.  Towards the middle of the book the relationship go better.  When they got to camp the relationship got stronger.  At camp they had opposite day and AJ and Arlo and the gang teamed up against Ms Janie their counselor to do everything opposite.  Their relationship became strong because they formed a team.  They stuck together.

AJ and Emily always had a good relationship, but there is not a lot of evidence.  Except they hugged each other.

AJ and Jamey met towards the end of the book, they never had a good relationship.  They were always fighting with each other and they never agreed on anything.  Jamey was the counselor and he wanted AJ to just listen to him and his rules.