Hmm, just to throw my interpretation out, it sounds like Dumbles, Molly, and Ginny plotted to marry her to Harry before the final battle and then, when Harry and Tom mutually took each other out, they'd split the Potter and Black fortunes. I presume Remus was in for something and attempted to control Harry's attitude and training such that it would be a mutual take-out and not a complete wipeout by a surviving Harry. Presumably, Harry found out about this and that generated the split before the big battle. With Neville alongside him, Harry went into the final battle and triumphed.
Author's response
- You're very close, but thinking in too small a time scale.