Kylo didn't take the shot, but didn't do anything about it ahead of time, either. If Kylo can get away with blue-on-bluing wingmen after, certainly before is an option. So is the Force, and so is the space radio. All of the subsequent "kill it if you have to" about your past, well, I think the distress is at his own weakness for not being able to do it.

"I was so upset" is not exculpatory about planetary scale genocide, and Kylo perfectly well could have killed Snoke and Hux and prevented the order from being given. (And even if I'm wrong about the "perfectly well", it's the sort of occasion where one might legitimately be expected to try. Especially if you think you have family at the target.) (Any view of Tuanul other than "blatant atrocity" supposes that the First Order has legitimacy as a governing power. Which they clearly don't themselves believe.)

I think there's a very basic error in thinking that it's appropriate to structure any story about this one special person and it doesn't really matter who dies, it matters how Special Person feels about it. It's just possible that The Last Jedi is a recognition that the Star Wars franchise has figured this out. I hope so.