I can answer that question!
You'll get a 500 baht fine (maybe more nowadays) for careless driving causing injury and you'll have to pay some compensation to each rider (few thousand each should do, but it depends on what they accept)
However, your insurance won't pay anything for their damages if they didn't have a tax sticker or a driver's license and if you were stupid enough to tell everyone in the room at the police station where you live or work, you should expect the grandparents to show up at your workplace or home moaning about how the insurance won't give them anything.
But that's pretty much it from my experience.