Will the four ancient beauties be very fat?

No, in the Tang Dynasty, being fat was the beauty (you can look at the pictures of ladies in art books, or the pictures of Zhang Guifei in the Tang Dynasty). Everyone else is slim (the book says that once, Xuanzong joked that Yang Guifei was compared with a beautiful woman in history, saying that the emperor wanted to protect that beautiful woman from being taken away by the wind, but I'm not afraid you would). This shows that women in other dynasties are quite slim.