The word their is a possessive pronoun. A pronoun takes the place of a noun, and a possessive pronoun shows ownership. Their acts like an adjective, describing a noun.
I mowed their lawn.
John found their dog.
Mom and Dad enjoyed their vacation.
The word theirs also shows ownership.
That lawn is theirs.
The dog is theirs.
The vacation is theirs.
Use the pronouns their and theirs to show ownership.
▶It’s your turn. Decide whether to use the word their or the word theirs in this sentence blank. Jan and Joseph love ____ new house. Did you figure it out? Good for you!