The answer to that would be the context of what you are reading. We, in the modern world, when we read modern publications understand the first, second, and third person tenses by the context of what is being said. This is no different with scripture. Realizing that the King James translators used the older English (thee, thou, thine, thy) to distinguish between the tenses, (for they were not speaking King James English on the streets of England in 1611), we in the modern world do not use those words and terms anymore.
In a nutshell, context will determine the use of "you" as a singular and "you" to a group of people.