Tonight, as the boys were in their beds, C stood bolt upright, leaned over, and said, "I want hug, M. Want hug, M. Kiss!"
This moment was unscripted, unprompted, and impromptu. It is, in my opinion, huge. C wanted an interaction with another child, with his sibling, and he asked for it.
Of course, M had no idea how to react: he stood there and reached out, and C grabbed his hand. That's okay. There's time, and there's hope.