DD (2) is called Alexandra. We don't really use a nickname for her, but she can;t pronounce her long name and calls herself Lily. Her older siblings have picked it up and call her Lily too. I quite like the nickname, it suits her well (although imho it't too "frilly" for a full name). I'm quite tempted to let the children use the nickname, but would it be too strange to call her another name - will she and everyone else be confused at the end?