I just tested a template of mine (Cell) which has the setting shown in the attached, for in the citation, ambiguous section of the output style. But if you have that set and you still have the author showing up, then you should copy and past the author info from one of the records to the other. It sounds like endnote isn’t convinced they are exactly the same, even if they appear to be the same - an extra space at the end or slight differences in the puntuation of the authors initials are enough to make endnote think they are different.
P.S. the order in the text is defined by the publishers, and usually is correct, despite that fact that esthetically we authors don’t like the appearance of c before a. It usually dependent on the alphabetical position of the first and subsequent authors, or title or year.
I had already copy/pasted the author name to make sure they were identical. Did it again, but still did not solve my problem.
However, I found thge solution: it’s because for the in-text citation I did not have the proper setting in the author name section. I needed to select ‘omit repeated authors’ - see attached.