His is a possessive pronoun and can be used both as a subject phrase and an object phrase. It can't be used alone as a subject or object, his requires the noun that belongs to the word.subject: His...
"He" is a subject pronoun, as in "He owns this car" where "he" is the subject of the action and "car" is the object. "His" or "him" are object pronouns, as in "This car belongs to him", or "This car...
"They" is a subject pronoun, since it is the opening word of the phrase. For example: They ate lunch. They played with me. If it was an object pronoun, it would read: I played with they. Since you...
You can be both a subject and an object pronoun. You have a nice car (subject). I will call you tomorrow (object). It and one can also be both subject and object.