I wish she just writes to him " while staying in this place, it seems that I have began to...

I think if Iyana mentions she has memory loss, her brother would definjtely do something extreme. From what we've gathered, he's the type of person that would set the entire place on fire if he hears word of Iyana being harmed. I think the safer route is to try and probe information without mentioning she was about to die when she first came to the novel and that she has no memories.