"¿Dónde se quedan ustedes?"
Translation:Where are you staying?
Why is the 'se' necessary. The sentence makes sense as: 'Donde quedan ustedes'
You have to use the reflexive form (quedarse) because the subject, ustedes, is performing the action of staying on themselves. So you need to include se as the pronoun that receives the action.
I believe it would be "te" if you were using the "tu" form of quedar (quedas), but since they are using the ustedes form (which means "you all", plural of "you"), the "te" changes to a "se" in this case.
Please correct me if I'm wrong someone!
Theo, i have learned from doing these lessons and reading the comments that the best way to answer your question is to think of it this way. Everytime you see "se" someone is doing something or feeling something to or within themselves.
So in rhis case look at it like this. "Where do you keep yourself"