EDIT: Okay I think y'all are misunderstanding "more than one applies." This is for one, singular Pokemon. So like, Mega Rayquaza is both a Mega and a Legendary. GMax Charizard is a Starter and a GMax. There aren't enough Pokemon like that to possibly account for 5% of the votes.
They learn their lesson and feel awful for their boys but this third normal kid is going to be neglected at several points in their life. They're basically gonna be raised like the parents' first born bc they are in no way prepared for a normal-kid upbringing
Kuniharu will expect so much of them (grades and chores, general helping out) and Kurumi will realize how even tho she's more loving, she still isn't as supportive as she hopes to be. This kid would be a learning experience for all of them!
Would kusuke still be competitive to a kid that young? When he realizes they're normal, I'm certain he'll think less of them. But would he try to get them to hate Kusuo too, even though he lives all the way in Britain?
Kusuo's first thoughts about them (imo) would be quick fondness but also apprehension. On one hand he's nervous abt everything that could go wrong- would the little sibling be scared? (Thanks kusuke for putting that thought in his brain, you jerk.) Would they end up depending on him too much like their dad?
But on the other hand he wants so bad to have a normal bond. He for sure helps raise this kid but he also knows he CANT let his parents rely on him for this. They need to learn (he knows all too well) but he really does want to make sure his little sib turns out good (physically healthy and as happy as they can be) and most of all he wants to be a good big brother.
Imagine Kuniharu and Kurumi with a normal third child. A child who needs nappies, a child that needs to be fed, a child that cannot walk, talk or solve problems semi-decently until they are like 5. A child that will cry when they need anything but will not be able to tell them what they need.
Imagine the total and utter shock when they realise just how much a regular child needs and how much they have not been giving to their eldest sons.