ok. let me help here. believe it or not, i get paid in rl to do this.. hahahaha
what you're describing here is not schizophrenia. Its Dissociative Identity Disorder--what we used to call Multiple Personality Disorder. The differences are sometimes confusing. However the symptoms are very different. Schizoph. is caused by genetics, we believe. DID is caused by severe childhood trauma, usually at a young age, where the multiple personalities were the only way the child could emotionally survive.
It is very possible for someone with DID to "integrate," and it is one of the accepted treatments. It takes a huge amount of time and work and consistency. It is not an easy journey. It is a coping skill to henious trauma. If you'd like, I could help you reflect that he was diagnosed w/ DID at one point but is now integrated and is functioning with one personality.
The upside that i can see is that he might have no respect for anyone who desires to harm someone else so brutally. And, he would be, probably, a strong defender of others who have been traumatized like he is. I think he could make a rather undeterable auror and would be a very cool character.
Does that make sense at all?
K.