Update now that the newest Smash DLC just announced a few days ago.
Smash Bros Ultimate Main
Maova - Sephiroth
Rosia - Any swordies
Yeig - Palutena (Probably spam Nair)
Vermilla - Marth
Kitori - Robin
Tana - Wolf
Belphi - Byleth
Reiza - Link (Any) (Change to Archer if he can be in the game [Or any Fate character for that matter. I can dream okay?])
Clara - Zelda
Rumel - Corrin
Lenna : Gets an adrenaline rush and wants to beat everyone. Gets very competitive, likely to beat you in racing or fighting games as such. In conclusion, don't underestimate her in this kind of manner. She may look like someone who doesn't play games, but in reality, she's a nerd.
Alphonse : Like his sister, Lenna, he would become very competitive. Searches for cheat codes online and plays dirty to win, but later would get exposed by Adrian. He's an expert in horror games (like Phasmophobia), would try to taunt the ghosts by challenging them into a fistfight.
Kalem : The lowest of the bunch, he can't even get past the tutorial part. But plays along to spend time with his younger siblings, for their sake.
Adrian : Analyzes each characters' ups and downs, also a master of remembering and executing difficult combos. He could have beaten Lenna easily but he purposely lets her win. But to others? This intellectual man would never back down his stance.
Julia : Falls in love with the characters that she would simply be simping. Uses characters as references for her work, would likely to cosplay one of them.
Alvar : Doesn't play games that much, but if he does... he would be pretty similar to Kalem. He's an expert at handling guns but can't work his way through a simplistic puzzle game. He just doesn't understand how this new world of entertainment works.
Blanche : He would yell continuously as he tried to fend off the other players' barraging attacks. Simply the type to rage quit, literally destroy the controller, and yells profanities
Mira : Uses characters by their looks, if she were to play Smash, she would choose either Kirby, Princess Peach, or anything cutesy. She does display some basic skills for fighting games.
Ludwig : Would be the most chill in playing games. Doesn't care if he wins or not, but it does matter whenever he sees Mira loses or Blanche winning. He would likely to sabotage Blanche purposely to let Mira win if the three of them played together.
Ethan : Like Adrian, he's a genius at debunking the game's system. Would throw off deceitful comments like "I can't really play games" or "I'm bad at it". Behind that smirk, he already set his target to humiliate you endlessly.
Well, first you need to explain how they work, then you need to explain the limits of the medium, then if it has any use for life improvement/warfare, and then Urainia and Umbrum will play one.
I feel that Umbrum would like those massive RPG-style games where you can do all sorts of stuff, while Urainia is perfectly fine playing Metro and Animal Crossing.
I would introduce them to Soulsborne just to make them suffer. The princes will probably find a way to do a no-damage speedrun like a boss. With no equipment.