Complex sentence: Some decades later, King Ferdinand II transformed the old refectory of the monks into a Pantheon for the Kings of the House of Braganza, with their tombs being transferred from the main chapel to this room.
Split into simpler sentences: Some decades later, King Ferdinand II transformed the monks' old refectory into a pantheon for the kings of the House of Braganza. Their tombs were transferred from the main chapel to this room.