Question

How to respond to van ustedes a la clase de arte

Answer 1

The question could be asking either one of two things:

1. "Are you going to art class?"
2. "Do you go to art class?"

The word "ustedes" means "you."

But it's the PLURAL form of "you."
We only only say "ustedes" when we're talking to more than one person, at the same time.

So, either way, to respond to this question, you would have to answer with "we." (Nosotros)

"Yes, we go to art class,"
or...."No, we do not go to art class."

Answer 2

Si, nosotros vamos a la clase de arte.