There's nothing that prevents two habitable planets existing within the goldilocks zone. With enough CO2, mass, and a magnetic field, Mars could have been habitable. A magnetic field would have made Venus habitable for a while.
The "turn intelligent life around the same time" part is suspect. Mankind went from realizing that those glowing things were planets to being able to visit them in less than one millionth of Earth's current lifespan. If you isolate the history to just animal life, it becomes slightly more than a millionth. Imagine closing your eyes, spinning twice, shooting a gun, and hitting a housefly five kilometers away, on purpose.
This is actually the subject of the Drake Equation, except that it is looking for life anywhere in the galaxy, so that one-in-a-million gets multiplied by all of the stars in the galaxy. There is a broad range of answers to this equation, but the current best guess is that there should be twenty or so intelligent civilizations in our galaxy. The chance of two being in the same solar system is vanishingly small.
Let's tip the balance in our favor a bit. If we presume that panspermia came by and seeded all of the planets a billion years ago, that narrows it down so that the other planet should have animal life on it when the first one figures out how to go visit.
If you theorize that both planets shared extinction events, then we can jigger the numbers so that both planets started their rise to intelligence 65 million years ago. If we expand mankind's "rise to intelligence" to a thousand years, then the chance of them rising to intelligence simultaneously drops to maybe 1 in 1000.
The thing that really kills your idea is that, even while sharing Earth, civilizations didn't experience technological rise at the same time. Around 70k years ago, Homo Sapiens were nearly killed off, but then we spread everywhere. The planet could easily currently be populated by Neanderthals or Homo Erectus, and our suspicions are that neither of them would have generated space flight by now.
So, you could hypothesize that we'd find something trainable on other planets, but the chances of us tripping over another space-faring civilization in our own solar system is virtually non-existent.