Vosotros is used in the majority of Spain, Equitorial Guinea, and Western Sahara and for ser would take the conjugation you note. The latter two have substantially smaller populations than Spain or any other Spanish-speaking country so they are often ignored in discussions on linguistic issues in Spanish (not to mention that in many if not most cases their Spanish-speakers are non-native).
In some parts of Andalucía, you will hear ustedes with a vosotros conjugation, but that is not considered part of Standard Spanish and is best to be avoided by people not from that region.
You can still hear vosotros used in parts of Latin America, but never as quotidian speech — it will always be in some sort of a heightened register (religious, poetic, ceremonial), and even then such uses of vosotros are rarer and rarer every day.