Hola,
I’m a native Spanish speaker from Spain (I live in the U.S., spoke English all my life with a native English speaking father and my English could be better than my Spanish). Since I am Spanish, we use vosotros. While I heard people in the U.S. learn “ustedes comen”, I would say “vosotros coméis”.
Castellano is the word we use to describe what they are taught in Spain, and Latin American Spanish is what we usually just call Spanish.
Nah, ambas terminas son correctas pero la RAE recomienda usar “español”.
“Castellano” is the word used for Spanish in general in many countries in Latin America though