Is it possible that one of these early homos is already the common ancestor between us and chimps? Or do we know that isn't the case (like through genetics or something)?
Homo itself, no. No way. The earliest known homonids, well, possible but very unlikely for two reasons:
1. The dates are wrong. The consensus dates for when humans and chimps split are about 1-3 million years before these fossils. However, the methods of dating are prone to error so it's possible - if unlikely.
2. All known hominids have derived traits not found in chimps. That is, they have features they share with us and/or later hominids but not with chimps or earlier apes. It is, again, possible that the chimp line evolved these traits but later reverted to the primitive state but it's unlikely.
(Note: primitive here just means in the ancestral state, it's the opposite of derived. For example, in humans, having five fingers and two eyes are primitive traits whilst bipediality and hairlessness are derived traits)