Main character and his 'sister' are adopted at different times. Step-Mom 38, Sister 20, MC 18 and still in High School (LOL). Since MC and sister are two years apart they could be adopted at different times. I personally think the supposed twist will be that the MC & sister are actual siblings and to further go down the rabbit hole that one of the MC's main fuck buddies is their biological Mum. I'm thinking Kelly, since she initially says that she's old enough to be MC's Mum. And secondly because she really loves the 'new' invention of the Morning After pill.
Cheers and have a champion day.
I don't think I've heard the school called high school, maybe I missed it. I thought it could be junior college, or some kind of vocational or business school. I also thought the same thing about Kelly, posibly a pregnancy back in her porn star days.