Emmy, Betsy, and Cecily do sound like sisters. :)
My favourite is Elizabeth (I unfortunately can't use it). One of the very few genuinely classic and timeless name imo, it isn't overused at all and there are so many adorable nicknames (I really like Effie, Bess, Betsy, Bizzie, Buffy, Izzy, Tess, Tibby, Zibby, Zizi, Bucky, Beth etc... But my favourite nicknames are probably Effie, Bucky, Buffy and Izzy)
Shoot, I think I just convinved myself to put Elizabeth on my list. oops.
Uhm, yes, back to you, OP 
Mary is nice. But Elizabeth is much nicer imo.