Despite what that article says, that’s not “unlike anything we’ve ever seen before”. All of the gas giants in our system have asteroids leading and trailing them by 60 degrees in their orbits. This might be the first time we’ve seen it with both bodies being planetary in size, but the principle is the same.
Yes, but it is interesting to imagine potentially habitable planets in the same orbit as each other.
The latest research indicates that KOI 730 (the star which supposedly had two planets in the same orbit) does not actually have them. Instead the two are in separate orbits. Here’s a blog about it: Kepler Finds Planets in Tight Dance
Having two planets of about the same size in L4/5 positions to each other is not stable, as I understand it. One has to be much larger than the other. However, you could have two with the same mass in a Janus-Epimetheus-type co-orbital relationship. The orbits would probably have to be extremely round for them to be stable.