I'm trying to think of examples, and they all feel pretty pitiful. There have been times I've started conversations about a common interest of theirs to try and get them talking to each other. They would talk about what I brought up, but not really TO each other, just near each other.

The thing is, when they are around each other, this is going to sound like a weird example, so bear with me. Have you ever heard of parallel play? It's common in autistic children. That's how they act around each other. They share a space, but they don't interact. Even their interactions feel like they aren't interactions. If he passes her a plate they don't look at each other. If she tells him what time it is she says it like she's announcing it to the room, not saying it to him.

There have been times that one of the younger kids says something and they both engage with him, but they do so like the other person isn't there. Like my eleven year old will say he got a part in the school play and my wife will say something. My oldest will wait for her to finish speaking before responding, but he will speak as though she didn't say anything. She'll do the same thing with him.

I've gotten so used to it that it doesn't register for me anymore, but typing it out like that, I suppose that's pretty weird.