How did Isaac and Miria became immortals?
Same way as Gandors and Martellos.


  Box with elixir of immortality went from what's-his-name brewer to Dallas Genoard, who then left it at Gandors' place. On Scilard's orders, Dallas recovered the box, but then he was robbed by Isaac &amp; Miria, who took the box with them to Firo's inauguration party, where all present drank the elixir.