A nonrestrictive modifier adds information that is not essential for the reader to understand the sentence. In case the nonrestrictive modifier is eliminated, the meaning would remain the same. Only nonrestrictive modifiers are separated by commas. Taking this into account, the sentences that contain correctly punctuated nonrestrictive modifiers are:
My oldest sister, Maria, is a pilot - If we remove <em>Maria</em>, we can still identify which sister we are talking about.
My two best friends, Tory and Monica, met me at the movies - If we remove <em>Tory and Monica</em>, we can still identify which two people we are referring to.
Bulldogs, which I love, are the cutest! - If we remove <em>which I love</em>, we can still identify which dogs we are talking about.
