Complex sentence: That evening the two main adjoining function rooms, the Peacock Room and Gransha Room, were packed with people of all ages attending dinner dances; including the hotel guests and staff, there was a total of 450 people inside the building.
Split into simpler sentences: That evening the two main adjoining function rooms, the Peacock Room and Gransha Room, were packed with people of all ages attending dinner dances. Including the hotel guests and staff, there was a total of 450 people inside the building.