In my family tree one couple named three of their daughters Mary after their mother. The first two died and then the third was named Mary Ann. Fortunately she survived - I think they had 18 children. Sometimes you find similar names in siblings if they are being named after other family members. It might be in your family that the parents had an aunt Susannah and a good friend Susan. My parents named my sister after an aunt and my brother after an uncle, with me she just like the name lol