I think the problem is , when reading this, we get the idea that they're not bad people and the original girl just never asked for help, or never tried to change for the better, and she was hostile and it cant be helped that the brothers neglected her-
Like
They're the good guys, they just never got the chance to prove that they're the good guys
If we accept the "unapologetic proud brothers oh so kind to give her a chance to prove herself" narrative the author is serving, then either they're the jerks, or the original girl was an asshole that deserved what she got
We end up victim-blaming at this point
Real family isnt suppose to pick and choose when to be there for each other- at the very least not in fiction, right?
Thats true. There are a lot of inconsistencies, but it strikes me as similar to life itself. People living in a household like that will often seperate themselves to an extent that they are near strangers. I've seen homes in which siblings havent talked to each other for months. So its not a stretch, these people living in different houses, to have not really interacted. So the interactions we were shown could be a result of that.
She was very much negleted in her house/building thing but that news probably didn't reach everyone else. If it did/when it did it was probably after the original mc lost herself & begun her self-destructive behavior. At such a point, with little interaction, it would makes sense that her family/grandfather/brothers only saw it as her being a villainous child or someone deseving of the actions that befall her.
So, the way I view the situation/the authors intention is that the fitst mc never really attempted to make any positive contact with the family. The second mc aims to make contact tho, not all positive of course. So. . Rather than the "proud but loving if you prove yourself" in regards to the siblings it strikes me as "wrong but redeemed" even if they don't realize they are wrong. So I agree with you but also thinks theres more? I feel its to soon to say who contributed the most to the situation.
And yeah? But for the most part people have the final say in who they regard as family. After all the full phrase is "the blood of the covenant is thinker than the water of the womb" which is shortened to "blood is thicker than water" a phrase that is as such HEAVILY misunderstood in my opinion. So my point it- you may be only half right in the grand scheme of things.
As a bonus. . If we criticize all who stood by then we get more people who walk away entirely. Thats what I think at least.

The idea that a victim of abuse needs to fit a certain behavior so theyre worthy of love
Like, hellooo
Toxic af?