Assuming everything is unlocked: Jaime plays Captain Falcon. Because he has the skill to take advantage of CF's powerful but finicky moveset, and because he likes shouting "FALCON PUNCH!" all the time like he were in an anime. Or possibly he plays Game & Watch. (If he doesn't, Paco does.)
Diana is playing Link. Because he's sensibly attired for arena combat. As she gets to know the game better, she'll switch over to Samus.