Okay since we are talking about Alone uhh here's what I picture:
I think Alone as a whole thinks of himself as one person because they have a shared consciousness- not like one guy with three heads, but three guys in one head (if that makes sense. Like three minds but they blend together so they are both separate and whole). It's broken fractured pieces of Ghost, who he was and what he could have been. It gets crowded and loud inside his head, a lot of trauma and confusion at war with itself, makes him stress out and prone to outbursts easily.
Lefty is the one on the far left when you look at him. Lefty's jaw doesn't work, his tongue just lolls out at all times and he drools incessantly. He's the least 'there' and can't talk much but gurgles and grunts plenty. Very impulsive and acts on instinct/whims.
Center definitely responds to Ghost. He's capable of the most speech and keeps the other two focused. He needs to keep himself in a state of semi-delusion, following orders and remaining loyal to his team. That he's still the person he was behind the mask, if he took it off he'd look normal again, this is just his Ghost persona, right? He acts like a monster so he dresses like a monster, but that doesn't mean he is one. Right?
Right = Riley. Riley is the one who is consistently reacting to emotional stimuli, still very much feeling like a little boy from Manchester who's scared of the dark. He needs a hug, actually. Ghost is always cruel to him, tells him to shut up for always crying or getting skittish, and Riley always tells Ghost he's just like their dad now.
But don't worry, usually they get along fine :)