I like
Mamie and
Maisie although I like
Mamie more than
Maisie. Like you I don't care for them as nns for
Mary and
Margaret. I think they're removed enough in sound from their original sources that I would use them as freestanding names and not nns.
“It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.”
~Mark Twain