In the US it would seem ustedes seems like it would be more like you all, or you guys/girls or y'all in the south.
Unless you are in spain, they have a informal plural form called vosotros. it is kinda cool, but not too popular.
Why is ustedes singular? I always thought usted was a formal way of sayin "you", but i keep missing the ustedes
If ustedes is 'you' then what would be considered "Y'all" besides Vosotros.