There being a polyamory route in this vn makes me so happy! its so rare to get poly rep and i happen to really like the characters involved too
On how to get there? Sure.
1: from either lake or jorgen's route, go with jorgen after y'all talk about his family
2: on the rooftop, when you ask about him and lake, say you think lake is a cutie
3: when they hug you in their room on day 3, say it feels right
4: when in the shower, choose to invite both of them to your room
There you go, that's all you have to do. For what it's worth, tho, I don't think it's a perfect route. It focuses more on jorgen than lake and I think it'd be better if it focused on both of them about equally. That said, it's still a nice route