Scan your WiFi for your computer PC or Mac and login in using the AppleTV app FileBrowserTV.
Navigate to your family photos folder.
Press the slideshow icon to the left.
Change your slideshow options: shuffle your photos, adjust the delay between photos and select a transition effect then press Start Slideshow. That's it.
Note: You can choose music files to play along with your slideshow, simply queue your music. When you hit Start Slideshow the music will play automatically.