You need add group tags with bracket to "Title" field of the media upload dialog.
Photo #1 Title: Bob [pet cat persian] Photo #2 Title: Nimo[pet fish clown anemonefish ] Photo #3 Title: Alice[friends female San Francisco CA US] Photo #4 Title: Without group tags
If you give a group option [galleria gid="pet"], only #1 and #2 will be displayed.
YES. Galleria WP V1.1(or laters) can display multiple galleries on a page. Restrictions : gallery use thumnail scroll options ( thumbnail = "top-scroll" or "bottom-scroll" ) should be placed the last position, otherwise automatic thumnail scroll will not work.