How does a character like Mrd. Croft differ from a character like Elizabeth or Mary Elliot?

I am assuming you're asking about Mrs. Croft. As the wife of Admiral Croft and sister of Edward and Frederick Wentworth, Mrs. Croft did not begin life with the luxuries and advantages of Elizabeth and Mary. None-the-less, she is portrayed and kind and amiable.

Elizabeth's personality would probably be seen as agreeable as Mrs. Croft's. Mary on the other hand was a bit harder to handle and often displayed defiance and temperamant.