Indefinite Pronouns

My attempt to make sense of the vagaries of the English indefinite pronoun:

1. Only singular:

Anybody, anyone, anything, everybody, everyone, everything, somebody, someone, something, another, each, either, neither, nobody, nothing.

These always take singular verbs.

E.g., Everyone is here. Neither of my parents is alive. Nobody in the world has the right to tell me what to do.

2. Only plural:

Both, few, several.

These always take plural verbs.

E.g., Both of my friends are here. Few of my friends are happy. Several of my children are in Chicago.

3. Portion indicators (sometimes singular, sometimes plural):

All, any, enough, less, little, more, much, none, plenty, some.

a. If these pronouns are used with things that cannot be counted, then they take a singular verb.
E.g., Some of my knowledge of grammar is useful.

b. If they can be counted, they take a plural verb.
E.g., Some of my friends are here.

c. In other words, if one can ask the question “how many,” then the pronoun is plural.