The instructions look to some part quite specific for the publication.
Do they just want the complete set of pictures in a PDF, or is there more layout involved?
Also, the instructions are not complete, as they should at least specify the color profile to be used, or they should refer to color settings. At the very, very least, they should say whether to submit the images as RGB (preferable), or CMYK (cause for issues).
That said, you'd better use Photoshop for exporting as PDF, because Photoshop uses the Adobe library for PDF creation, which is far superior than what Apple uses in Preview.app.
If they want layout, they should provide templates, or at least guidelines.