Both Peter and Anne don't get along with their mothers mainly because of the generation gap seprating teenagers and parents. Peter is embarrassed with his mother because she fights with the father in front of everyone. Anne and Margot understand their mother tries her best, but Anne is still much closer to her father as he teaches her, laughes with her, and is overall a more relax kind of parent. Margot's and Anne's mother is more strict as she scolds them when making noice in the Annex.
A. Best the reason why it is not better (even though it sounds right) is because it says "out of the five cousins" there for we are comparing ben to five other people and he is the best.