"Nosotros estamos hablando en la clase."

Yes, it's correct. There are a couple different forms of the present that you can use.

We speak/talk = hablamos (present)

We are speaking/talking = estamos hablando (present continuous)

Yeah. I don't know why it's "do" on the end now..

In the dictionary, both to speak and to talk is translated as hablar, and I use it for both regardless of the audience. The context usually clarifies who is being addressed. Dirigir is also use when speaking of addressing an audience and perhaps is a little more specific. For to say I use decir.