Alright, you’ve got [thread=238901]Trojan Earths[/thread], and then you’ve got two Earths which are in each others’ L4/L5 points. I don’t know if this latter situation is stable. I suspect it is, but one assumption of Laplace’s restricted 3-body problem is that the third body has a negligible mass compared to the other two, whereas in this case the two smaller bodies are of comparable mass. That may change the problem enough to screw it up; I don’t know.
If you had two or more earth-like planets in orbit around a gas giant in the comfort-zone that ‘might’ work, (especially if the gas giant does not have a strong magnetic field)
but such large moons would cause quite a bit of tidal heating in each other.
(which is why I only put one around Gamma Cephei b)http://www.orionsarm.com/worlds/Silence.html…
in a system with a slightly brighter star than our Sun, the comfort zone/habitable zone would be wider, and so two Earth-like planets could be accomodated fairly easily;
once life has established a biosphere containing oxygen, the feedback mechanisms in the atmosphere could maintain a habitable range of temperatures as they have on Earth over hundreds of millions of years.
The planet further from the star could have a higher CO2 component in the atmosphere, and be kept warm by global warming;
while the brighter sunlight on the closer planet might increase the rate of photosynthesis and remove some of the greenhouse effect.
Such a finely balanced pair of worlds would be rare and unusual, in my opinion;
however it certainly seems likely that a solar system could have several candidates for terraforming, so that a solar system with many artificially produced earth-like worlds is a definite possibility, given the technology and the will.
like this one
Well, they haven’t ever been proven to be unstable, have they? The only variable thatt would affect the equalibrium is the mass of the parent body compared to the others, right? Of course, I’m probably totally wrong in that layperson assumption.
Although I also wonder about each body getting enough water when condensing into planets. Or did the Earth get its water later? Like from comets or something?
That first part was in reply to Achernar, who’s nicely worded explanations are always appreciated by this non scientist type person. 
No, as far as I know, they’ve never been proven unstable, and I suspect that they are, in fact, stable. However, what we’re dealing with here is a 3-body problem, and the 3-body problem is surprisingly (and notoriously) hard to solve. So it might be that it’s been worked out and I’ve just never seen the solution, but it might be that nobody knows the solution, ie, whether it’s stable.
“All these worlds are yours, except…” (You knew somebody was going to do it sooner or later, didn’t you? ;))