Vocabulary: difference between «all» and «everything» and position of «all» as a pronoun.

Hello, 

While correcting one activity in the book, 4b on page 27, we have come across (nos hemos encontrado) con «all». I explained that the position of «all» in a sentence (when we say «tod@s nosotr@s/ell@s/vosotr@s) depends on the verb. If the verb is a lexical verb, «all» goes before the lexical verb, and if the verb is an auxiliary verb, «all» goes after the auxiliary verb.  Here «all» is a pronoun 

We are (auxiliary verb) all drinking.  (= All of us are drinking)

We all (lexical verb) enjoyed the party. (=All of us enjoyed the party)

After this explanation, Encarni Girón asked me if we could say «We ate all», and I said «no». Why? Go on the following link to understand the difference between «all» and «everything».