What personal pronouns are their?

The Word 'they' is a personal pronoun.

A personal pronoun is a Word that takes the place of a noun for a specific person or thing.

The personal pronoun 'they' takes the place of a plural noun, or two or more nouns as the subject of a sentence or a clause.

Examples:

The Browns came to visit and they brought the new baby.

Jack and Jane came to visit and they brought the new baby.

The houses on this street are vintage. They are all at least eighty years old.

The houses when they were built were in an elite section of town.