Um it said in this chapter that he wasn't aware of his uncle and aunt's past transgressions?
He has been in contact with the head maid so he should have a bit of information. And if I was mistaken about that, would it hurt to drop by check if your only family is alive or not? or have someone to check the situation? I'm not sure of this, but before she reincarnated, she died without seeing him and that's just not right.
Now that I read the recent update, looks like he entrusted her protection to someone who cannot protect her. and I was right with the "I aM Not StROnG EnOuGH"
Her brother better have a good excuse for not showing up until now, not that "I DoNt HaVE EnoUGh PoWER" kind of bullshit. Our girl has been through a lot, I totally understand why she has been timid from the past. I hope she gets free from the parasites soon.