Complex sentence: One painter, by the name of Pantoleon, who may be referred to in other documents of time, seems to have been in charge of the group, who probably worked together in a workshop connected to the Imperial court.
Split into simpler sentences: One painter, by the name of Pantoleon, who may be referred to in other documents of the time, seems to have been in charge of the group. They likely worked together in a workshop connected to the Imperial court.