[For a great number of the questions, there's little she can offer in way of explanation. Clearly the question in regards to Ichiru's brother is only something that Zero can answer himself. However... ]
I would say that you each are more similar to Zero than the opposite.
[Very much so. Ichiru, despite all his flaws, has never shown very much hatred toward vampires in general.]
I can't answer much for Zero and his brother. [She'll leave that to him, and rightfully so.] But I can tell you more about vampires within our world.
[After all, she very much understands the needs and desires of a vampire herself.]
We aren't the only vampires within this place. But we are in the majority, and recently outside of ourselves, numbers have dwindled. There are certainly more humans than vampires, but we aren't the only supernatural creatures.
[Demons and other supernatural beings have and do inhabit the dome. She pauses, looking back and forth between the boys before continuing on]
In our world, there are different types of vampires but in general our consumption and need for blood is the same, with a few exceptions. Blood tablets are widely used, and while I don't find them very sating, they help curb the thirst we experience for blood.
[They certainly aren't a cure, but in a pinch can be useful, even if she finds them unpleasant.]
If done with consent a vampire can feed from a human, which may be done among most the vampires classes. But most humans are not aware of the existence of vampires, so it is also considered a little taboo. [Well... more likely, vampires that drink from humans erase their memories after.]
More often, the most sating blood that one can drink is from their significant other, friends, or family. So I tend to believe that it is more likely that vampires drink from other vampires. That's the case for all of us within this house. And for my father, myself, and Ai, our fangs are poisonous, so we would be unable to drink from anyone other than another vampire without various consequences.
[The pureblood certainly have various difficulties when it comes to such. She glances to Zero...]
Your other questions though, I can't really answer for him...