Quote 1
What would I have been if things had turned out differently? (18.71)
This is a question any of the characters could ask – really, it's a question any of us readers could ask too – but it's especially poignant coming from Chris, who will always be in a wheelchair. At this point in the novel, he's still imprisoned by his body, to the point where he can't always control his speech or his movements, and he worries that his medical condition has deprived him of the chance to create an identity that wouldn't suffer from these medical, physical, and financial burdens.
Quote 2
Gloomy tomb of a room--Theo will make a good writer someday, Chris thought. He wouldn't spoil this wonderful, spooky Halloween story by telling him about the real person up there, the one with the limp. (3.48)
Here we have competing stories. Theo shares his with Chris using elaborate combinations of words, and Chris recognizes this as proof of Theo's future career. He hesitates to "spoil" Theo's ideas by relating what he knows really happened. In a way, though, the story Chris doesn't tell is just as out there and spooky. As the silent watcher, Chris knows more about what the real story of what's happening over in the Westing house than aspiring writer Theo does. He may be shy, too, about the fact that (at this point) he can't communicate his version of the story with the ease and ability that Theo can.
Quote 3
"Itsss-oo-nn," Chris announced.
"What did he say?"
"He said it's snowing," Theo and Flora Baumbach explained at the same time. (5.24-26)
This moment shows us the separations there can be between language in thoughts and language in speech, as well as in understanding different kinds of speech. Chris's medical condition keeps him from articulating ideas in ways some people can understand, but we know from the text's POV/narrative voice that he has very articulate inner thoughts. While we know the reason Theo's able to interpret Chris's speech – he's had plenty of practice as a caregiver – we don't know Flora's. We'll find out later that she had a disabled daughter, but for now this just creates a sense of mystery around her character.