Sentence:  But Mother and Father and Grandpa and Grandma and Uncle and Aunty couldn't very well call out "Millicent Margaret Amanda" every time they wanted her, so they shortened it to "Milly-<WSD>Molly</WSD>-Mandy" which is quite easy to say. 
Meaning of the word marked with <WSD> tags:  (Mary) "or, less often," '''Margaret'''.