What do you mean these two people are only good at books and paintings?

What do you mean these two people are good at painting and calligraphy? It means that neither of them is good at painting and calligraphy.

These two people mean two people and only represent one. Being good at painting and calligraphy means being good at painting and calligraphy, which is a problem.

Being good at painting and calligraphy means having both painting and calligraphy, and being versatile. This sentence shows that these two people not only can play calligraphy and painting, but also have many other talents, so they are very talented people.