I'd say that this is a mixed bag of a game, some mechanics make sense, others do not.
The drawback is that there's a lack of interactions between certain characters main and otherwise, and it's quite complicated or in other aspects rather intermingled resulting in a slightly confusing story telling format. I'd really advise this guy take a moment to really hammer out a primary story-line and make everything else secondary or optional to achieve a better result, that way you'd streamline the game down to the core and allow for content to be more flexible.
As for the platform being RPGM well it's not the worst platform, I can say this much right now, I'm suspecting its due to the scale of what he's attempting to do that there's so many bugs involved. Including one which immediately crashed my game after a scene.
Ren'Py has its own issues, not to mention making a highly complicated game using that would seriously chop down on interaction, basically its a slide show game at that point, but it'd be easier in other ways to make use of it. It's really dependent on what you want to achieve as a developer and writer, big hint, sacrifice complexity for simplicity, or more quality for less content.
You can't have both.
You'd have to plan everything from scratch at the very beginning and then build outwards with serious consideration to making the story engaging without losing interest. This is coming from a hobby fanfic writer, it's easier said than done.
As for Unity's engine, how much time and effort do you think you'd want to sink into Unity, depending on whether or not your aim is an RPG or a full on story telling game. I'd recommend anyone undertaking Unity only if they're freaking ambitious with their aims, and planning on making something really engaging or interesting, not really just story telling but ingenuitive.