Trills and Klingons can't have children without genetic manipulation which would not have been available on the planet.
With resources at the station, Bashir could help Jadzia & Worf have children (see 'Tears of the Prophets'), but not on the planet.
And we know that Klingons can breed with humans (see TNG 'The Emissary' and Star Trek: Voyager). Klingons and Klingon/human hybrids can even continue to have children (see TNG 'Reunion').
So, obviously, Jadzia & Worf had an open marriage. They loved each other but had sex with human members of the crew to keep the colony goin'.