Baby brother

I've mentioned Bright Eyes' little brother a few times, but I don't think I've told you that the two of them just don't get on!
It's not the little one's fault. He wants to play. He shows empathy when Bright Eyes is having a tantrum. He looks for him in the morning when he wakes up. He calls him "Ca-ca". It's really cute.
I just wonder how long his enthusiasm will last for, given that Bright Eyes hits, pushes or headbutts him at every single opportunity he can find. If I have the two boys in a room together, I have to be there with them, because it will only take one minute before one of them is yelling, either from frustration or from pain.
This is probably a normal sibling reaction, but I think it may be exacerbated by the fact that the baby represents uncertainty for Bright Eyes and dealing with him requires more flexibility than he is capable of... and that's the autism talking.