You've posted in the Premiere Elements forum, dee. There are actually several ways to create a slideshow using Premiere Elements, Photoshop Elements and the Organizer. So it depends which program you want to use and how automatic you want the process.
Since you're looking for photos that include the two of them, it would be helpful to know if you've assigned People tags to all of your photos in the Organizer. If so, it will be very simple to locate photos of them togehter.
If you have not, you'll need to manually gather the photos yourself and build your slideshow using either the Organizer's slideshow creator, Premiere Elemetns' slideshow creator, Premiere Elements' Video Story tool or by gathering the photos on a Premiere Elements timeline.