Is were an indefinite pronoun

No, the Word "were" is a verb, a form of the verb to be.

The Word "were" is a plural, past tense verb or auxiliary verb.

Examples:

They were so young when they married.

We were planning to leave on Friday if all went well.

A pronoun is a Word that takes the place of a noun in a sentence.

An indefinite pronoun is a Word that takes the place of a noun for people, things, or amounts that are unknown or unnamed.

The indefinite pronouns are: all, another, any, anybody, anyone, anything, both, each, either, enough, everybody, everyone, everything, few, fewer, less, little, many, more, most, much, neither, nobody, no one, nothing, none, one, other, others, several, some, somebody, someone, something, such, and they (people in general).

Example: You may have some, there is more in the kitchen.