] This family is intensely competitive and selfish and just plain mean to each other. The only time they cooperate is when they have a common goal, which is invariably to another’s detriment.

I get the impression that this family’s malice is not that well coordinate.
Isabella might be clever enough to think and plan towards her goals, but I can’t quite see her confiding in John or trusting him to help her execute her plans. She more likely manipulated him to think that the whole scheme is to his advantage. Possibly even suggested to John that Catherine is totally in love with him.. (Just writing the horrid idea sends ants up my spine...)

] I do not like this family.