I think that this is the better practice if you're going to see two of them, although I think it would be fine to talk about them if it moves you or would be helpful for you to do so. You don't need to disclose any information that would identify them and of course, if you don't sign a release of information, they can't break your confidentiality.

When I told my T that I had consulted with another T, and this was after about 6 years of therapy, he was absolutely fine with it, said it was unnecessary to share any information about it, and displayed no interest in knowing who it was or whether I ever saw "her" again. I suspect that the involvement of more than one T at any given time in therapy may be more common than is thought. I don't think it's a problem to see whoever you want whenever you want to see them, and however you want to communicate (or don't) about the other(s). Just do what is best for you.