From what i remember he is not killing Gretchen because of her son - he asked him the first time to agree to do what he tolds him and he will keep his mother alive for now! That's his motivation for MC - to make sure he will cooperate,but now the dissappointment of MC to his mother grew bigger after finding all that time she was fucking his bully behind his back and she enjoyed it,so now it's no longer sure if MC will decide to give up of his mother and say something like "she is no my mother anymore" since he feels too humiliated by her and started to hate her! Who knows,Savannah may be the one to convice him to give up and renounce on her! As for Savannah,she likes to be the center of attention,to have fun with whoever she wants and do what she wants without carring for anything and anyone and to make people always agree with her and do what she asks them for,so if she really did find out about what her brother's doing she may come to a deal with him after treaten him to give him to the police if he don't accept her offer which probaly will be something like he stops acting like a father person to her and let her have fun and do anything she wants with whoever she wants and support her when she needs him and in exchange she will turn her eyes off and pretend she doesn't know anything about what he's doing and let him keep act like some pscyho serial killer if that's what he really wants to be (may be even helps him finding girls/womans fucking black guys) - sounds pretty convicing especially the fact that they are familly and sooner or later familly always find out about other memebers of the familly are doing and then they talk about that to see if they can come to a deal and in the past before their mother dissapear(been killed) Clyde was always been supportive to his sister Savannah but after finding what their mother was doing he changed,mostly because of his father of course! Of course that's only one theory,it may happen that Savannah still doesn't know anything about any of that and as you can see not always familly keeps suporting each other when something bad happens - Gretchen humiliated her own son by fucking his bully and enjoy doing it and now it seems like he may not be able to forgive her and instead to give up on her; Savannah may also decide that she will no longer support her own brother if she still doesn't know what he is doing and suddenly happens to find out about it...
PS: I've just tought of a way how Savannah may decide to humiliate Gretchen with her son(she is already doing it by making her son believes they are in a relationship while she makes him either cuckold or cuckoldry depending of what he says to her about she been non-exclusive to him) - What if at some point she decide to convice him to change himself since right now everyone sees him as a insecure,poor little looser that they can use and humiliate all the time because he is weak and will not do anything about it and for that she convice him to do a surgery and change his sex from a guy to a girl and that way to become more confident and find out how much power he will have as a girl and how instead trying to humiliate him everyone will flirt and try to have fun with? Imagine the reaction of Gretchen when she comes to Savannah to search for her son and Savannah shows her that she doesn't have a son but a daughter instead

and that her son/daughter tells her that because of Savannah now he is no longer feeling like a looser who everyone can humilate all the time and that may be now he/she will find out why they like black guys so much and may be if that happens he/she will find a way to forgive Gretchen for humiliating him by fucking his bully... There will be one more girl for this black guys because of Savannah and it will be the perfect and biggest humiliation to Gretchen ever

But of course it will still have the option for the MC to accept or to not accept Savannah's offer about that so everyone can play it the way they want! Of course that's only a idea but still since the game is focused on racism and humiliating i think this will fit perfectly well if the developer sees it here and decide to do it and gives the players that option too - may be as end of the season and beginning of the second season if there's a next one! What do you think?