Is they a plural pronoun

Yes, the pronoun 'they' is a plural pronoun; a Word that takes the place of a plural noun or pronoun, or two or more nouns or pronouns.

The pronoun 'they' is a subject pronoun, a Word that functions as the subject of a sentence or a clause.

The corresponding plural object pronoun is them, a Word that functions as the object of a verb or a preposition.

Examples:

The Johnsons came for a visit and theybrought the baby with them.

Jack and Jill came for a visit and theybrought the baby with them.