The Bibienas were the most influential Italian designers of the 18th century. Spanning three generations, seven members of the family were scenic designers. One of the three major innovations by them was:

Introduction of baroque art

Explanation:

The Bibienas were the most influential Italian designers of the 18th century. Spanning three generations, seven members of the family were scenic designers. One of the three major innovations by them was: the introduction of baroque art.

The Baroque is a style of architecture, music, dance, painting, sculpture and other arts that flourished in Europe from the early 17th century until the 1740s (Wikipedia)

Bibienas family three major innovation : the introduction of baroque art, vast scale and elaborate ornamentation and use of angle perspective.