A Man and His Dragons

Many years prior, our protagonist, a petty thief in some fantasy desert kingdom, stole two wyvern eggs from a rich merchant about to ship them to faraway lands. He originally planned to make a fortune by reselling them, but they hatched before he could, and his soft heart made him take care of them until they could fend for themselves. Much like wolves, wyverns live in small packs (or flocks?) made of the member of the same family; they commonly form very strong bonds, so the siblings stayed together in adulthood. They now roam their territory in the desert, while their adoptive father pay them a visit from time to time.