All humans have weaknesses - surely the Pevensies do too! Now to find what they are.....
Peter should have been able to handle Edmund better - though Ed wasn't making it easy for him! Also, he shouldn't have led his siblings to hide when Edmund broke the window. And he didn't believe Lucy when she said she saw Aslan....
Susan should have been nicer and more motherly to Edmund and Lucy. She, also, should not have
hid from Mrs. Macready and led the others to do the same. Especially, she should have kept believing in Narnia!
Edmund was always being sour - he could have been a lot nicer if he tried! When Lucy told the others he had gone to Narnia, too, Edmund just told they were playing a game; and broke Lucy's heart. Also, don't talk to strangers, especially those who seem evil! Edmund should not have accepted food from the White Witch, besides. Yet, he could have made it OK, by telling Peter and the rest of his siblings. But he didn't.
Lucy does not have many faults. The only one I can think of is that she could have been a little less fussy the first time when the others didn't believe her.
I think is the order of them, from weakest to strongest.