Complex sentence: As Hyacinth and his three companions traveled back to Kraków, he set up new monasteries with his companions as superiors, until finally he was the only one left to continue on to Kraków.
Split into simpler sentences: As Hyacinth and his three companions traveled back to Kraków, he set up new monasteries. His companions were chosen to be the superiors for new monasteries founded by Hyacinth as they proceeded, until finally he was the only one left, and he continued on to Kraków.