Comment by PaulHoule

Try a simpler game. I think a lot of people think TTRPG = D&D and the world is worse off for it.

There are numerous tactics that work to face the "not serious" problems you have in a game for "young adults".

For instance, serious players get resentful when somebody not serious comes in late, forgets their character sheet, etc. You could lose either or both of them, but with a little prep you don't have to. In Paranoia it's easy to shove a preroll into their hands, give them a 1-2 minute briefing from "The Computer" and build up tension around this character who mysteriously appears (and if the new player complains that they don't know the rules tell them they're not allowed to know the rules!)

Toon is the epitome of "not serious" and, like the other two games I've mentioned, is a game where you can buy one book and have everything you need, including your first scenario.