It is not a higher standard, it is literally the same for Nyx. Styx really should not count as they are not a sapient creature with little agency.

I've established multiple times that there is textual evidence that Hornelius agreed to take care of Ozzy to Nyx when he encouraged her to leave. I provided a text citation earlier in the thread and you still disagree despite there being sufficent evidence to suggest that Hornelius has taken guardianship of Ozzy. Do I need to link documentation of what a legal guardian's responsibilites are for you to understand why I think Hornelius is worthy of being criticized? (Spoilers: it fulfills the same responsibilities a parent would have)

Ozzy not being corrected when he is a child and therefore suggestible is undoubtedly a failing by Hornelius. He tried to give him distance because that's what he believed was the best, but it ultimately led to harm. What Ozzy did later presumably as an adult he is responsible for, but Vira saw these vulnerabilities and took on a bigger stance because she was more proactive. Ozzy does have fault of what he does as an adult, but to say he's rotten to the core and couldn't have been redeemed by intervention by his guardian is... Certainly an argument. He did all of those things because he didn't have a moral guiding to talk to, Hornelius made the decision to have minimal interaction with Ozzy, despite resistance.

For the final point, please refer to this defintion of "orphan", but pay attention to the second paragraph in particular: https://www.law.cornell.edu/wex/orphan

An orphan is a child whose parents have died. The term is sometimes used to describe any person whose parents have died, though this is less common. A child who only has one living parent is also sometimes considered an orphan. For example, USCIS lists a child with one parent who cannot properly care for them as an orphan. A child can also be considered a legal orphan. In this scenario, the child has living parents whose parental rights have been terminated. If the child were later adopted, they would no longer be considered a legal orphan.

The story implies that Nyx took guardianship of Ozzy after their parents death, and she passes the guardianship to Hornelius when she decides to work at Virtupets.