Higher tracks take precedence over lower. If a full-screen image is on track 1 and another immediately above it on track 2 only track 2 will be seen.
To merge them try picture-in-picture - scaling the track 2 image down to make it smaller to allow track one to show in the background.
If the image on track 2 has high contrast, chromakey (green screen) effect can be used to remove its background, with a result like this...

If instead the TRANSPARENCY effect is applied to track 2, the two tracks will be blended together but neither will be at their full video level.
If this isn't what you want, describe the result you're aiming for in more detail.