Unpopular opinion, I think his mom somehow can be "save" from her darkness, after all we know that she isn't used to be like this. Idk how, but i think there is a way...
But in Yuri's case, I think Souta and her can't meet eye to eye already. Well it's never happen in the first place.
I am assuming the difference between those two character is about the care they have for Souta, Mom sure care about his Son, although in a weird way. But Yuri is... nope.