The battle of the three Marys of Dún Laoghaire

HOW do you solve a problem like Maria? It’s one of the songs sung by Julie Andrews in The Sound of Music — which, if you don’t delve into the politics of the plot, tells the story of a young blonde woman who managed to win the love of another woman’s children.
Out in Dún Laoghaire, the trinity of Marys (only one of whom takes the Latin form) is causing major problems.