I'm listening to an audio version of The Three Musketeers. The narrator pronounces their names as
POR-thos, A-thos, AR-a-miss, and dar-TAN-yon. It seems to me that they should be pronounced
por-tos (not sure which syllable is accented), ah-tos (ditto), ar-a-MEE (not men's cologne), and dar-tan-YON.