What a strange start. It's like the author took several romcom tropes, mashed them together, and started the story in the middle. Take the popular GalXOtaku, ALSO make them step-siblings, ALSO skip the "getting to know each other/will they won't they" phase, deport their parents to remove chaperones... Do we get to know the characters or do we just assume they are amalgamated clichés?
I'm wondering what this story is about. Is it them finding a way to tell their friends and "come out" at school? Are they going to graduate and go to college and find jobs? Or is it a gap slice of life where they act like strangers at school, then they go home and he feeds her and they flirt? There has to be some angle that gives the story teeth. It's only one chapter so Im'ma let them cook (Hey-ohhhhh!) but this is either genre-bending or a slow-moving car crash.
One final thing. Given the set up, in my mind there is zero chance they aren't banging. Two unchaperoned teens are doing what their bodies tell them to do. If the author doesn't acknowledge this, my disbelief is suspended.