You have posted this question in reference but I believe by these character names you are referring to the work of literature entitled Animal Farm.
From the beginning of the book to the end, you have one unchanged character. Clover cares and wants to nurture the other animals but because of her lack of intelligence throughout can only slightly remember what the original rules were and is quickly and easily convinced of other rules or ideas.
Napoleon grows more and more power hungry throughout the book. In the beginning, he agrees with the ideals of Animalism, but as the book continues, he cares not for the people or the rules and changes both to suit his needs and desires.
Squealer is fairly consistent as he is manipulated by Napoleon to manipulate the other animals. As Napoleon's hunger for power grows, so does Squealer's ability to convince the animals.
Benjamin does grow throughout the text. For the majority of the text he remains a consistently wise donkey. He sees through Napoleon's antics, but doesn't act on them until it matters to him personally. This only occurs when Boxer's life is threatened. But Benjamin's actions arrive too late.