Not only can you skip the mom's sex scene, but you also have the option not to have sex altogether. If you still had to watch despite being given, two chances to avoid it, that's on you.
Finished the Alexis path, and meh. It's just all sex all the time. I know this is a sex game, but that shit gets boring after a while. You know that they have too much sex when Nyx has to give Alexis a period just to stop them from fucking, and even then, MC gets a blowjob. The only thing of interest is that Alexis's parents know Santi is Mc's father.