It's personal preference, really. What you like isn't what I'll like. I don't know why Margot is popular. To me it's awful. Marge and margarine. Margaret is horrible as well, like porridge. I don't like Monroe for a personal name - it feels nondescript and has nothing going for it, yet also seems pretentious and contrived, like names for cars. And reminds me of the phrase 'bagging Monroes' which for Scots and other mountain enthusiasts means climbing the Scottish peaks over 3000 feet.
Anastasia, no. It feels old and unappealing. And I dread to think of the pronunciations and spellings it will call forth. With Adeline, I don't know it. Is it French? Could be a bit like something medicinal, though. Adele is better, I think.
For M, I'd prefer Matilda or Mary or Miriam, Milly...I can't think... Just throwing out names here: Miranda, Minerva, Millicent, Marina, Melanie, Mireille, Mavis, Melinda, Mylene, Maya, Minny - oh, that mouse, so no. Molly, Monica, Mona.
You could go for the adjacent letter L, still keeping them next to each other but without duplicating and causing confusion with both being M. Lucy or Lucia (lu chee a), Leonora, Leontia, Leona, Lara or Larissa, Lulu, Lisa, Louise or Louisa. Lucinda, Lorinda. Lindy. Loretta. Lois. Lorraine. Laura, Lauren. Leticia. Not saying I like all of these, but just trying to think of names.