Margaret and Rose are very good for their time.  Girls were often named after the two little princesses, Elizabeth and Margaret Rose. Phyllis was my mother's name ;she was born the same year as Princess Elizabeth (our late Queen). I'm not sure how common it was.  Perhaps Susan Elizabeth?

I like the others!

@coracle 

Susan Elizabeth would actually be a good one. They may have been popular girls names at the time.

I think Polly Anne and Lucy Rose could also be an reference to the four children that C.S Lewis originally named- Ann (though spelled differently), Martin, Rose, and Peter.

And I would imagine that the royals in the different regions of Narnia would have two middle names, as it is kind of common for upper class to have two middle names.

@jasmine_tarkheena I had so many schoolfriends with an Auntie Margaret. Elizabeth is Biblical of course, but I'm sure that the Elizabeths I knew in my age group and older were from the Princess.

Not everyone had a middle name; my parents and their siblings didn't.

Elizabeth is the name of the mother of John the Baptist and the cousin of Mary, the mother of Jesus. I think it grew into popuarlity in the 15th or 16th century, perhaps for Queen Elizabeth I. I have a cousin named Elizabeth, and three of my cousins are named Andrea Elizabeth, Jordan Elizabeth, and Kylie Elizabeth. So it kind of runs in our family.

Perhaps for the royals of Narnia, Frank Martin Thomas and Helen Victoria Julia (perhaps in reference to Queen Victoria, which happens to be the last year of her reign when The Magician's Nephew takes place).

I like the idea of other Children of Adam and Eve from Earth-cultures having middle names, but I am not sure how popular the practice would be among Narnian Humans. Is it a thing in Archenland, or in Calormen, or the Isles?

...I do like Rose for Lucy. I need to think about what middle name I would like for Susan.

Posted by: @silverlily

I like the idea of other Children of Adam and Eve from Earth-cultures having middle names, but I am not sure how popular the practice would be among Narnian Humans. Is it a thing in Archenland, or in Calormen, or the Isles?

...I do like Rose for Lucy. I need to think about what middle name I would like for Susan.

I think different cultures uses middle names differently. So it wouldn't be surprised if the different countries like Archenland and Calormen use the middle names differently than in Narnia. That is, if it is a thing.