Alix was "Aunt Alix" to her nieces, both Alicky and Ella called her by that name (not to mention Missy who has a chapter on her in her bio). Yes, both Alix and Minny use "motherdear" to their own children (Minny also extented an invitation to Alicky to call her "Motherdear" in one of her letters to her son Nicky.).
That would make sense. They were devoted to their Danish friends.