Complex sentence: The windows on each floor are of a different equally ornate design, the largest however are those on the first floor, which are in the form of a trefoil, the emblem of the Tresham family.
Split into simpler sentences: The windows on each floor are of a different equally ornate design. The largest are those on the first floor, in the form of a trefoil, which was the emblem of the Tresham family.