And Rei reaction at the end is confusing : Is he upset or happy about Youta challenge ?!
He is happy about Youta challenging him again, but anxious about losing, this seems to hint at all the previous competitions actually having come down to close calls, but Youta having an inferiority complex feeling that he never stood a chance
As for why he is worried about losing? probably because his entire outer personality has centered about being perfect outside, and he is probably not ready to let the mask fall, which means that it is actually for his own good to lose, he can't keep that facade forever and it is not healthy anyways, but it is kind of too early for that amount of character development to happen just 10 chapters in, unless we are getting axed
Also since the parents know how much of a slob the older brother is at home, they probably don't think the younger one would develop an inferiority complex given the fact that well... the older brother is actually not perfect, but a slob, so in their minds they have 2 great kids that balance each other, and the younger one even landed himself a cute girlfriend, and as thus for them it would never register that there is a sibling rivalry or that one would have grown a complex against the other
Even more it would be pretty hard for them to figure out that Youta has been avoiding women, because all the girls that approach him were after his brother, which is something that only Youta and probably his closest male friends know