Kyosuke will be the boss of Rival Schools 3, with Kurow as his DragonKyosuke, heartbroken over losing his twin brother Hyo, snaps and either sets out to take over the world (or try and revive his brother) to cope. He'll hire Kurow to be a second in command, since he likely has some secrets from the assassin group that coule help in the plans. Kurow helps, but only he could use whatever Kyosuke's plans are to further his own goals of taking over the world (he doesn't kill Kyosuke since he wants to overthrow the assassin group, so he continues to ignore his original order).
Yurika and Kurow's father is The MedicYurika inhereits the Medic's musical ability (somebody who's able to play a violin song out of a freakin' bonesaw has to have musical genius that be passed on to a child) and her clothing seems to be inspired by German culture, while Kurow inherits his sadistic personality and obsession with sharp weaponry. Per the Gratuitous German trope, German culture influenced Japan quite a bit - perhaps after his work with RED (or BLU) finished, the Medic settled in his homeland's former Axis ally and married a Japanese woman.
Roy is the self taught student of Terry BogardIt's possible that Roy either met Terry in person, or saw one of his matches. Either way, he was so impressed, that he decided to emulate Terry's style but, his renditions of Terry's signature moves are imperfected; likely because he lacks proper tutelage. Yet, he hasn't let it deter him. Instead, he's made the style his own by combining it with what he'd already learned as a star quarterback.