Re: "There are over 200 roads that cross the border."
Buildings, roads, and properties that cross borders are probably the least of your problems. Famously the Haskell Library/Opera House(Auditorium) in Derby Line, VT/Stanstead, QC not only straddles the US-Canadian border, it was deliberately built that way. https://en.wikipedia.org/wiki/Haskell_Free_Library_and_Opera_House The Mohawks manage to somehow control a modest territory including parts of New York, Ontario and Quebec. If they can keep two countries, a US state and two Canadian provinces at bay, I expect the Irish can work something out provided they don't get too much help from Westminster and Brussels.