Hi,
For clips already in the timeline, to remove the zooming effect select the clip by clicking on it, and then click on the crop tool (the one that looks like intersecting angles) in the tool bar at the upper right of your screen. In the crop tools that appear, remove the Ken Burns zooming effect by selecting the "Fit" option. ( I'm not sure, but you may be able to select all of the clips as a group and select "Fit" for all of them at once.)
For a default "Fit" selection that applies to all clips, before you begin the project click on iMovie/Preferences. In the preferences box that appears, choose the "Fit" option under the heading Photo Placement. That will cause all clips that are added to the project thereafter to be without the Ken Burns zoom effect.
Regarding your audio question, to make any audio clip play as background throughout the movie, select the clip and do Edit/Copy and then do Edit/Paste and then repeat Paste . . . Paste . . . Paste . . of the clip in the audio well throughout the movie.
-- Rich