Madame Tussauds New York has added a wax figure of Shiloh Nouvel Jolie-Pitt to their museum's display of the likenesses of Angelina Jolie and Brad Pitt.

This sentence contains an error in pronoun/antecedent agreement. The antecedent of the plural pronoun "their" is the singular "Madame Tussauds New York."

While companies and organizations are composed of groups of people, the names of these groups are considered to be singular. Use a singular pronoun to refer to the singular "Madame Tussauds New York," which is the name of a company.

Madame Tussauds New York has added a wax figure of Shiloh Nouvel Jolie-Pitt to its museum's display of the likenesses of Angelina Jolie and Brad Pitt.

Notice that in the original sentence, while the pronoun ("their") is plural, the verb ("has added") is singular. To many people, the use of the singular verb with the name of a company or organization sounds correct while the use of the plural pronoun seems fine. Remember that both the verb and the pronoun associated with the name of a company or organization should be singular.