They won’t be stepbrothers whatsoever because if you think about it properly they are already both grown adults with their lives if you never meet someone they’re not really your family you don’t know them in the first place and they don’t even have the same blood anyways it’s their parents just because your parent marry someone and less you’re living in the same house in structurally speaking at some point or another this person is in knowledge is your sibling to use yourself then that probably is that but they are grown so no And I’m pretty sure the our top has his father’s name in his registry or the mom’s maiden name and he’s not gonna change it only because she’s getting married

bro why did the author feel the need to try and make them step-brothers? outta all the tropes