1. I really like the name
Mary. I think it is pretty and it ages well. Also it isn't used a lot nowadays, so it would be fresh as well as classic.
2. I don't like the nn
Molly for
Mary. I just don't think it works. I think
Mary is just fine on its own, or if I used it I would probably call her Maidie.
3. If you want to call her
Molly, just call her
Molly. It saves confusion all round!
4. I like
Mary Elizabeth and if its a family name I say go for it! I wouldn't personally use it because it would seem very royal family-ish to me as there were royal siblings
Queen Mary I and
Queen Elizabeth I and there have been lots of repetition of
Mary and
Elizabeth together. I am English, though, so that could explain it.
5. Not
Elizabeth! I think most classic or traditional names go well with
Mary, nothing too modern or creative.