[@Strawberry425] Hmm, okay. I [i]think[/i] that clears it up. Would it be alright to say that my character has a mental image of what his twin looks like? So while he can't 'see' his twin, he pictures him as looking a certain way? This would be no more 'real' than a mental image of a situation while you read. 

As well, during intense experiences such as arguments or 'fights' between the two, would it be possible for the host twin to 'see' a glimpse of their twin in a human form? It could remain ambiguous whether or not this is a hallucination of a mind under extreme stress or an image imposed by the twin, if that makes any sense. 

In any case, I have a character nearly done. Thank you for your help!