All scenes work fine. (except handjob, I will redraw this scene later). You just need 30, 40 and higher lust for them.
Lust when reaching 100 turns into "Nymphomania". For now, the mechanics of nymphomania do not work (according to the idea, nymphomania will change the dialogues and make the sister more active, for example, she herself can initiate sex)
Regarding the coop game, this is a known bug (the fix will be released today), you need to give her the game first, and then play (it's my fault that it doesn't work)