@Scott-Rindenow Hi, that's not an easy one to answer directly because there's so many options available in editing,

'dissolve still photos' - Photos can be faded or composited by the opacity level, faded in/out using the transition handles on the end of each Object (photo, video, audio etc). there's a bunch of built in transitions, fading & compositing can be applied & keyframed with fxs like Chromakey, Masks can be added & used as transitions & compositing.....

not disturb the audio track

What has dissolving photos got to do with the audio?

I think for the dissolving you need to provide more information, you can upload screenshots of the VPX UI using the little arrow button next to the smiley at the top of a new comment, or watch the Tutorials at the top of this forum.