I like all your name options but have you considered that they would get post addressed with the same name, so both would get letters addressed to Miss M Surname and they won't know who should open it. My sister and I had this problem for years and it caused a lot of fights with things that were private. Not all people who write will use a full name or know a middle initial. Maybe it won't be a problem with more post going electronic but thought I would mention it.