Assuming that all of the planets are inhabited by life, here's what I'd see as the most likely situation.
The first space faring civilization would completely control and dominate the system without any other sentient races in the picture.
Life emerged on earth 4.1 billion years ago. The first evidence of tool use dates back 2.5 million years. We first went to space 56 years ago.
Extrapolating from the only example we have - very soon after life evolves to the point of general intelligence and tool use, we progress to a stage where interplanetary colonization is possible. When the first species to develop space flight goes to visit these other life-bearing worlds they wouldn't even find basic civilization, because if any other world had progressed as far as tool use first they would have already colonized the others.
Hope this helps!