Two directors listed, seems like a mistake - it that enough to delete one of them?

The way I understand it, if you are auditing credits, and the on-screen credits say "Directed by LeVar Burton" while IMDb says "Directors: Rene Auberjonois, LeVar Burton", you can assume that the error is in IMDb and submit a deletion for Rene's credit.

If Rene had been an uncredited director on the episode, then the person who submitted his credit ought to have given him an (uncredited) attribute. They didn't. Therefore, the person must have thought Rene was credited. But he wasn't. So the submitter must have been wrong. It's understandable that this error could have been made, since both Rene and LeVar were actors on Star Trek: Deep Space Nine and each of them directed a number of episodes of it.

So, in short, in a situation like this, rely on the on-screen credits when they are explicitly contradicted by the IMDb credits; don't assume that the IMDb credits are mostly correct but missing an (uncredited) attribute. This is particularly true for a director credit -- most dramatic television episodes have exactly one director. If exactly one director is listed on screen, that's usually how many directors the episode actually had.