
What happened to the lady and her son? Did they die ?

I think they are alive and the ambulance found them

I think it's not clear on purpose. We just see an ambulance but if that means they are collecting the mother and son injured or dead we probably never know... I think the author wants to have us guessing.
I doubt Sangwoo would leave a witness though after that interaction with the mother. She and the boy could recognize him.

why the fuck did he cover up the boy’s eyes with snow

I think he was fueled by impulse, thrown off by the resemblance this woman carried and the situation now presented to him. It's not completely logical because of the many ways the snow on his eyes could fail to prevent seeing the murder but if the boy woke up, I imagine he'd be in a state of confusion, unaware of where he was before he was knocked unconcious by the fall. On top of that, he's most likely sustained injury and therefore less likely to move as much or as fast as he'd like to tear the goggles off. Crushing the woman's windpipe can't have taken that long either. Maybe Sangwoo believes visual triggers aren't as influential as auditory ones, especially those you may not be able to recognize the sound of. The kids already in an unexpected outcome of this skiing trip. Either way I'm sure the boy will be traumatized. It's a small mercy to not have seen it but I don't praise the action in the slightest because it's made through abuse born psychosis. It's terrible circumstances.
All of my ideas are theoretical anyway so that was just my interpretation.

I don't think that's what matters to him though. He could've blinded the kid for all he cares. I think he's "protecting" his mental state in some fucked up way because he believes that's worse pain than physical. I could be wrong as hell though because I don't have enough information to get in the mindset of this particular serial killer.
Sorry for the dumb question but... Why do they make such a big deal over Love knowing how to fight..? Like alright he can fight but it’s not like he’s harming anyone now
Mm well the 'big deal' is not that he knows how to fight, but that he never told anyone, and that would make his friends feel a little betrayed, like he didn't trust them enough and kept things from them. The only one who thinks that being able to fight is a big deal is Love himself, because of his past (he desperately wants to 'belong', but since he could never belong anywhere BECAUSE of his fighting, this time he wanted to start a new life and didn't tell them, while still feeling guilty about it). Hope this was clear enough and not even more confusing for you >_<
He wanted to belong somewhere and he wanted to do so by not telling them that he could fight. Since he hid that fact though, he didn't want to tell them the truth because he felt like he was betraying them by not telling it in the first place. He also can't tell anyone what happened in the past because he just doesn't want to explain himself and let people know what happened and make them understand, make them emapthize.