Even veteran writers check the MLA handbook. No one memorizes all this. The rule of thumb is: two authors = both names; three or more = first name + et al.
Stick a sticky note on your monitor. “2 names = full. 3+ = et al.” You’ll never second-guess again. I promise.
And if you mess up? It’s fine. MLA is a guide, not a trap. Your professor or boss mostly cares that you tried. A small error in formatting is way better than forgetting to credit someone entirely.
