I think the writer has a thing for incest...their other work (snare of words? Sorry can't remember the English title) also have incest in it, although there was no explicit showing of a sexual act, the brother is genuinely in love with the older one and so is their uncle to their father. They also have this thing of making you think that maybe...just maybe one of the brothers were adopted (questionable bg, difference of treatment within family) then clarifying that they are 100% siblings.
I think the writer want this as their signature 😅