I'm answering these in the order they appear in my inbox so they might overlap or contradict each other as I read more of the comments.

That sounds like a great flashback scene. I'll be looking forward to that reveal.

This chapter could be right after the bombing (the recruiter scene) and he could flashback to when they were kids when he's thinking about Kalen being dead. It would be kind of sad--show that he really did love his brother--but after he doesn't get to be a soldier it will really make their conflict seem more real. The reader will want to know how they got from that caring older brother when they were kids to wanting to kill each other in the next chapter. Then you can slowly reveal that with flashbacks using the other scenes (and maybe some new madeup ones of their past).

That could work effectively.