Hi Greg…
Let’s make a basic distinction here…
the final output of what you are making is a video clip.
that means the width and height of the output will be fixed for the entire length of the file, regardless of the difference in resolution of various sources.
it doesn’t have to be 1920 x 1080, but whatever it is, it needs to stay that way for the entire video.
within those rules. as each image appears in sequence it is possible to animate it in some way to pass the image across the screen (scaling or moving) to create the Ken burns style effect you cite in your opening request.
if what you are seeking is to create is a “traditional” slide show where images can be various resolutions….then….nope you are in the wrong product.
Power Point would prob be more what you are looking for.
hth,
Alex