I just came across a question in another forum regarding the stability of a rather strange system. A huge methane-molecule-like system with the parent star in the place of carbon, and the planets in the place of H atoms (It's actually for a sci-fi story). If the planets moved in the same direction (that's what the OP said), what are the parameters in terms of mass, radius of orbit etc for this system to be stable. Also the planets should have a g-value so that humans could survive. I'm guessing that if it started out as a normal system, i.e. with the planets in a plane, then it should have had a violent past for the planets to go elsewhere. I also think that collision(s) should have been fine-tuned to form such a system.