I want a separate one about the brothers relationship now

I feel like it wont be as eventful tho. Jealousy? They're already married. Rivals? Already married. Kazuhisa's life is secured, so is Alex's.
Next is what? Have kids. Don't think they need 5 chapters for that.
Their story would need a plot (have kids), theme (have kids), conflict (?), etc.
Unless of course they just said they decided to get married but they're not married yet.
But, yeah. Their baby journey is a oneshot at best. Better to have their chapters scattered in the main characters' story.

hmm, that's true, but seeing their kids would be nice.