There is a very high probability the sister is dead. When they talk about what they want at the end of the world, the brother says he wants to spend time with his family and the sister says she wants to grant him his wish. I don't think there's anything much deeper there; just that her brother used to make her feel like he made a small little world just for her and so she's now doing the same, making him feel like this small little world (where he can spend time with his dead sister) is just for him.
Also, I want a Jeff Goldblum machine sister too. ;---;
Wait a minute. In the voynich hotel, there were two people eating a panda in one of the rooms, and she said she’d eat a panda with the one she loves if they asked. Might be overthinking it. Oh well.