1) Since you are publishing your tree from Family Tree Builder, you can only add information in the program, and not online. You can read more about that here:
2) To Associate a photo in Family Tree Builder, go to the photos section, double click on the relevant photo, go to the association tab and add the association.
In the online family site, you can tag a photo in the Photos and Videos page. Click on the relevant photo, and click on 'Add another person'
