
If i were the MC, i would have moved out.
Yeah, sure. The brothers have their circumstances, but the MC isn’t really asking or expecting for too much except for them to clean their own mess? in their own house? Didn’t the MC also suffered all those years when they were absent/incapacitated?
Rather than brothers spoiling their sister, i say this is leaning more to the trope where the author wants to show how much the people around the protagonists struggle with

I dont get the sympathy for the new guy? He slept with someone just because he finds it annoying that a girl is desperately clinging and begging him. He never talked to the guy who he claims to be his “bestfriend” about it nor did he doubted or clarified about the break-up. And to think he immediately slept with girl who his “bestfriend” just broke up with.
Why are all the good mystery novels on hiatus