Modify > Font Families is new to Dreamweaver CS6. It doesn't exist in Dreamweaver CS5.
To edit the font list in earlier versions of Dreamweaver click the item at the bottom of the list of fonts. One place you can do this is in the CSS section of the Property inspector.
Select the fonts in the Available Fonts list, and click the double chevron to move them to the Chosen fonts list. Japanese example shown.
Europe, Middle East and Africa