Is them third person

Yes, the Word 'them' is the third person, the ones spoken about.

The pronoun 'them' is the plural, objective, third person pronoun which takes the place of a plural noun or two or more nouns as the object of a verb or a preposition.

Examples:

I like grapes and I eat themwith almost every meal. (direct object of the verb 'eat')

Jack and Jill were there and I had a chance to speak to them. (object of the preposition 'to')