I'm pretty busy with my girls today, so I only had time for a quick look-see. One thing that struck me was your comment about a massive planet in the same orbit as a smaller one. That would work. Mass is irrelevant to an orbital path and speed, for the same reason it's irrelevant to how fast something falls to the ground. Of course, if the Earth is too close to the massive planet, then all hell will break loose between them, with the Earth being the bigger loser.
I'll read it all more carefully later.