Don’t do anything stupid is all I can say. As white foreigners the older one might get away with it, but:
1. Getting in trouble with Japanese law enforcement as a foreigner is a very bad idea as they can hold you without cause for as long as they want. Again, likelihood is nothing will happen but is that a risk they’re willing to take, and it will come back to you as their parent. There’s a pretty strong anti-foreigner vibe right now, too. FYI.
2. I don’t want to encourage bad behavior.
3. You gotta be chill and not act stupid. Don’t make a scene and be quiet. Foreign tourists are constantly doing stupid shit and ruining it for the rest of us. People live in Tokyo so as much as it might seem like a magical silly land of weird shit, it’s their home.
If they wanna drink, grab them some cans at a conbini and chill at the place you’re staying. Or order them a beer while you’re out as a family. Much greater likelihood when you’re all out. And as long as the 17 year old doesn’t look super young.