There IS a difference. No matter what people try to tell you, or convince you, there just is. Charlie is more compatible with Doug and I, behavior-wise, because he is similar to us genetically. Roman has behaviors that, because of his genetics and environment when he was a baby, we find mystifying. We struggle daily trying to figure out what parts of Roman are just "him" and we have to adapt to. Sometimes we get so frustrated with a behavior and upon reflection later, realize that he has always been that way and probably always will be.
I often wish we had a biological kid before we adopted Roman. I think we would have noticed much earlier that Roman wasn't like "regular" kids. On the other hand, we just soak up any affection given from Charlie because we never got it from Roman. Roman is also learning from Charlie, both in playtime and affection-wise. We have noticed that he is giving kisses and being slightly more spontaneous in telling us sweet things; I think it's more because he sees Charlie than he actually feels these things. Who knows, though.
When playing with Charlie, as I've seen this week as they've been each other's only playmates, Roman is demonstrating much more imagination. His therapist has mentioned that emotionally Roman is really behind - more like a 5 year old than an almost-8 year old. He can fake it well with his peers, but he really does love to talk to and play with his stuffed animals and is right with Charlie when they play "guys." Coming to terms with this has been tough, but finally adapting to what he needs (even if we think it's weird) seems to have worked. He definitely understands what is "okay to do at home."