Assuming that all of the planets are inhabited by life here's the most likely situation.
The first space faring civilization would completely control and dominate all the planets without any other peoples at all.
Let's look at the evidence. Life emerged on earth 4.1 billion years ago. The first evidence of tools date back to 2.5 million years ago. We first went to space 56 years ago. If you still don't see what I'm getting at it's this:
Very soon after life evolves tools we progress to a stage where colonization is possible. When the first species to develop space flight goes to visit these other life bearing worlds they won't even find basic civilization, because if any other world had developed tool use first they would have already colonized the others.
This is a kinda clunky answer so comment if you need more clarity.