Mrs. Thomas was the woman who scrubbed Anne's parents' house when she was a baby. She took Anne at four months old, after both her parents died. Her reasons weren't selfless, though. She kept Anne to care for her children, which Anne did until Mr. Thomas died.
Mrs. Hammond was the woman Anne was passed off to. She's the mother of three sets of twins that she expects Anne to care for. That's a lot of diapers. When her husband died, she left Anne in an orphan asylum.
Mrs. Blewett is was the woman who wants to take Anne off Marilla's hands until Marilla puts her off. Blewett also has several children and is known for being "a terrible worker and driver" (6.11) with a temper. Good for Marilla for not trusting her.
All three of these women treat (or plan to treat) Anne badly, and see her as cheap labor rather than a child to be cared for.