You know, thinking about it, if the twins had come to Weston together, I actually wonder if R-Ciel, and O-Ciel, would have ended up in the same house. Because I see O-Ciel ending up in Blue, like he did, but I think R-Ciel could have ended up in Red house, or even Green house, if he had showed the necessary abilities. In the end, R-Ciel would probably have gotten himself, or O-Ciel transferred so they could be in the same house though. Not saying R-C isn't smart enough for Blue house, but... ehh
Hello! And well, Vincent was in Blue House, our!Ciel ended up in Blue House so I think Real!Ciel would have ended in Blue House too, or in Red House for a second possibility.
We might not see the twin reading as much as our!Ciel, but he’s good at chess and I’m sure they’re both as clever.
So I think they would have ended in the same house :) and as you said, I doubt real!Ciel would have let the school separate him from his brother anyway (and we know how he feels about the fag system).
Have a nice day!