As set up, NLM has the citation author lists set as if 3 or more, list 2 in both first and subsequent settings. (see image). you would need to change the two to a one in both spots, save as a new style and use that style in your word ribbon. You also need to add the et al. text to each (as shown in image and attached modified style).
I made the changes (and also changed the bibliography number to be in square brackets rather than parentheses, since that was what you showed and it was different in my NLM.