It's actually traditionally 1 cup exactly here (scoop a measuring cup out of the rice cooker per plate). Most people in my house are 2-3x daily, I'm 1-2x daily because I didn't grow up eating rice (I prefer bread). We have 2 rice cookers going at dinner because 1 one is for the dogs exclusively.
I'm putting my money on more people (8-10) but eating less than 200g per meal (1/2 cup uncooked, ~100g for most people)
EDIT, just saw sibling, that's impressive for 5 people, unless the dogs eat a lot of rice too.