For my current purposes, assume we have two planets identical to earth. So, could two of these planets form a stable binary system, and still be close enough to see the green foliage on the surface of the other planet? They would ideally not be tidal locked. If this is possible, how would it affect the day/night cycle and seasons? (If you don't mind taking it into account, I intended for these planets to rotate a binary star system, in which both stars are nearly identical.)
In Grimm's World the "moon" was a another world with visible continents and weather and even visible wildfires. Other than being very interesting to observe and affecting the culture of the people, it had no effect on the description of the planet in terms of having a dinural cycle, seasons, etc.
If you want to get more realistic, you can look at the Hill Sphere of a planet to see how far away a companion might be. If the distance is farther to compensate for the increased mass, so the tidal forces are no greater than what we have here, then you can postulate a day-length like ours rather than have tidal locking.
An alternative would be to have two planets in the same orbit around the sun, so they approach and receed in cycles. This would avoid tidal locking issues.
The way the moon formed was that something big collided with early Earth when things were still pretty gooey, and knocked a big chunk out, which then fell into orbit instead of drifting away or falling back to earth.
If you had a planetary mass that was somewhere between 2 and 3 earths, and hit it with a big rock so that it split fairly equally, then sure, why not.