I was thinking about these characters last night, and now that I've thought about it, I hope that none of them are the main rivals, or any sort of rivals. I'd rather these 3 characters were sort of like the DPt Stat Trainers, except a lot more relevent to the story. We could still battle each of them, say about 3 times each, but also pair up with them quite a lot. There teams could be themed rather than based on stats though, like how Colress had a technology/futuristic theme. Judging from their appearance, I'd say the big guy could have a food themed team, the ginger kid a tech team, and the girl could have a 'cutesy' team.
Obviously we would also have a proper rival (maybe a jerk) who gets the starter strong aganst yours who we battles around 6-8 times, and then the opposite gender character could get the starter weak to yours. Maybe they could make a sort of Brenden/May and Lucas/Dawn mash up for this character, where they're not all that relevent to the overall plot but provide us with useful information and give us items etc (like Lucas/Dawn) but we also get the occasional battles with them once in a while (akin to Brenden/May).