I like
Marnie a lot actually. It is an under appreciated name that has lots of nice qualities- lovely meaning, easily pronounceable, uncommon but known. I also think it ages a lot better that a lot of other girls names ending with an -ee sound. They did really nicely.
I'm also kind of partial to
Ethel. I think it is a pretty name.
Ethel and
Marnie sound so sweet as sisters.