Yes I agree with all of this, it needs a total rewrite because none of it makes sense. She should be heavily conflicted about what she is doing and full of regrets but either 1)can't help herself after being constantly pursued by Tobey or 2) he has some kind of blackmail or social pressure on her to give in to him. Both would be infinitely better than the stupid treehouse conversation where she suddenly acts like a 16 year old. Absolute nonsense.
There's the makings of a great game in here but the motivations for the story are ludicrous. Even with the old guy, she should still be heavily conflicted as to what she is doing.
These would be my changes:-
Adi and Mia would be step children, Adi with John and Mia with Christine, both from previous relationships obviously and this solves the cest issue.
The blackmail plot would be Christine giving Tobey extra tutoring and in a moment of weakness she kisses Tobey and it gets recorded by Henry and he uses it to his and his compatriots advantage with a secondary element being the bullying of Adi which would stop if she complied.
This also would be the start of the Tobey relationship.
The potential of losing her job and stopping her sons bullying would be the motivation for what she was doing.
Adi would also blackmail Christine, same way as Henry after catching her doing things with Goro and he would also ask for sexual favours.
Losing her marriage would be the motivation for not complying.