Indeed, nothing was established onscreen about either.
In the Lit, however, "The Officers' Club" states that Pohl died of malnutrition in the refugee camps. Reon is a focus character in the story, and it turns out...
Either way, Nerys was not close to him because she blamed him for not doing anything to help Pohl.
As for Jadzia's sister Ziranne, she appears in the story "Reflections" in the collection The Lives of Dax