To further her cause.

"Ok so since you are not the brightest I will give you a hint I came in her coffee twice thinking of two things that will really help turn the family dynamic around. Now I'm not going to tell you but i want you to at least try to figure it out. oh and if you think she will tell you not even she knows yet." and with that your sister turns back to the table and grabs the empty coffee mugs and puts them in the dishwasher. You walk over to your mother and say hello and make general small talk. You get the idea that you should test if last night she got effected by the pasta so you make a joke about having a big dick.

"HAHHAHAHAAH, you think I would believe that you, the boy that I raised and saw his little shrimp dick would have a big cock?" with that you believe that maybe you have started to figure out one of the traits your sister gave her and decide that you don't want to deal with any more of this humiliation so you say goodbye and leave. For the rest of the day you distract yourself by playing some video games and at night have dinner with the family where it doesn't seem like anything has changed so you go back to your room. Later that night you hear a muffled argument coming from your parents room and then silence for a bit, you wonder what they were arguing about but then after awhile you start to hear your mum moan really loudly and screaming obscenities. You manage to fall asleep by putting on your headphones and watching some youtube.