Here is the book’s description from the Amazon website:
This is the First book in a series of parallel worlds adventures. It follows the story of Nicole and Martin Sherman’s strangely acquired ability to travel at will from dimention to dimention in geographically similar worlds.
Their first stop, though unintentional, is the ancient island of Crete, in the Aegean Sea between Greece and Turkey where they are quite shocked to find thenselves in the bodies of two young centaurs.
They befriend the other centaurs on the island, all of whom are not native to it since they were brought over under false promises in order to serve their new masters’ hidden agenda of rebuilding their population by mating with the centaurs.
Nicole and Martin quickly uncover the Gogian’s secret plans and help the enraged centaurs get rid of their opressors and become a nation under their own rule.