If I am discussing two authors with the same last name, do I always need to provide the first name when I refer to the authors in my prose?
If you discuss two authors who have the same last name, provide both the first and last names at first mention. Thereafter, provide both the first and last names if there is ever any ambiguity about whom you might mean. Your in-text citations should always include the first initial along with the last name, or, if the first initials of two authors are the same, the full first name along with the last name (MLA Handbook 55).
No hard-and-fast rule applies in this case. You should simply try to make your prose clear to your readers, and including the full names of authors can sometimes provide clarity.
MLA Handbook. 8th ed., Modern Language Association of America, 2016.