There's no Benkei route. I don't know who started saying there was one. I will say it again, there's no Benkei route. You only get a H-scene with her in Koyuki's route if you make the right choice, and it has as much influence as choosing to do a threesome with Margrit and Chris in Majikoi, Chris route. In other words, it has no influence.
And about Tsubame, unfortunately, I still don't understand her route well. What I do know is that...
That's it, unfortunately. Source from guys who understood Tsubame's route. That's the only thing they said.