Ustedes vs. Vosotros
I've heard that people in Mexico only use Uds., while people in Spain use them based on the formality needed. Is this true?
Also, if being used on formality, how do we know when to use which? If there are two people in a group, one you know well, and one who is a complete stranger, do you use vosotros or ustedes?
P.S. Sorry if this is a repeat question. I couldn't find anything like it via searching.
You are correct about "vosotros" being used almost exclusively in Spain. To Latin Americans it sounds archaic; the closest example I can give would be the old "thee" and "thou" in English.
Generally speaking, if you are on a first name basis with everyone in a group, use the "vosotros". (Remember - this is generally speaking). It is correct that if there is one person in the group that would be addressed as "usted" in the singular, then you must use "ustedes" with the entire group.
Keep in mind that it's OK to make a mistake. Spaniards are very generous toward people who try to speak Spanish. If you make a mistake, just apologize and carry on. Nobody will be offended!
I think I would rather err on the side of formality. I would rather have someone tell me I am being to formal and say to me, "just call me tú," than for a native speaker to be offended by my lack of respect.
Well, unless you are traveling to Spain, it is good to know the vosotros form, but not necessary. Vosotros is actually an informal way of addressing two or more people that you know.
Assuming that you will not be needing that, let's concentrate on Ustedes. This is the formal way of addressing two or more people. This usually includes people who are older than you, teachers or people you don't know. Once in a while, I'm sure you might run into a situation where you know one person, but not the other, but not often. When in doubt, use the formal ustedes. Your friend will understand why you are doing this, so you don't have to worry.
Actually, "thee" and "thou" are familiar conjugations of "you." At one time, English had formal & familiar just as many languages have today. True: Spain uses "Vosotros" and The Americas "Ustedes." There is no familiar conjugation for 2 or more "Tu," so either Vosotros or Ustedes must be used when addressing 2 or more familiar people, as well as unfamiliar people.
...Ustedes.... This is the formal way of addressing two or more people.
This is also the informal way to address two or more people.