The parents are to blame.

How could anyone hate the brothers? They lost their sister, and then their parents straight up replaced their sis with a look-a-like. Not only that, but the parents show favouritism and bias to the adopted child, always taking her side instead of the actual children.

The brothers don’t seem to get much love from their parents, so it’s normal for them to feel jealousy or even hatred towards the adopted child. Why should they like someone that stole their parents’ love from them, and is replacing their dead sister.
That doesn’t make their actions right, but it explains why they bully her.

Also, the fact that the dad hit the oldest (Eugene) for no good reason (he just ate her candy damn) makes the parents seem more shady than they already are. Possibly Eugene was preventing her from eating the candy bc it was related to the death of their sister (Eugene is pretty mature, so there’s likely another reason behind the candy thing).

The parents are so disappointing.