Is there anything wrong with "Do you look at yourselves in the mirror?"? Is there maybe a preposition (auf?) required to make it mean that?
I'm pretty sure if it were changed to ansehen it would work (something like "Seht ihr euch selber im Spiegel an?") but not about sehen on its own.
"Sich" with a plural subject can also be used for "each other" (i.e., they see each other in the mirror). The "selber" makes it clear that they are each seeing themselves, not each other.
The "selber" isn't necessary for singular "er," since obviously that distinction doesn't need to be made for one person.
Why would "Can" be better than "Do"? I'm a native English speaker - those have different meanings, but only "Do" is an appropriate translation of the German sentence. Nothing about the German sentence asks about the feasibility of seeing yourselves in the mirror. "Can" would mean is it possible for your to see yourselves. "Do" means, is it currently happening. I say "Do you see yourself in the mirror" all the time with very small children.
I'm still confused by the "ihr euch selber". The translation says it's like "you yourself". I'm English we have "Do you see yourselves in the mirror". That's 2 references to the you, in the thing that is looking and the thing that is in the mirror. What is the point of the third "you/yourself" I'm German. What is this rule and where can I learn more about it?