Blurred/Feathered edges between two images

The project I will be editing will be in split screen close to 50% of the time. I would like to achieve a feathered or blurred look between two images.

The soft edges video filter doesn't seem to work well because I crop my images - it references my original edge line rather than my new cropped edge line.

Is there a way to make a natural looking blur between the two? Almost like a gradient? An area specific superimpose?

Thanks!