Edit one of the 5184 x 3456 images to the timeline. Once it is on the timeline, double click on it to open it in the Viewer. In the Viewer, click on the Motion Tab, and the adjust the Scale and Center parameters until you have the picture as you want within the framing of the 1920X1080 sequence.
Click on the clip in the timeline that you just adjusted to select it again and copy it (Command + C).
Now edit the remaining 5184 x 3456 images to the timeline. Once they are there, select them all - with the exception of the one you have adjusted. Once they are selected, control-click on any one of the selected clips and from the drop down menu choose Paste Attributes.
When the Paste Attributes pane opens, check the box for Basic Motion and click OK.
Now all the images should be set the same as your first image.
Repeat the process with the 4928 x 3264 images.
Once you have the images as you want, select them all and nest them (Sequence > Nest Items . . .) and then apply the Widescreen effect to the nest (Effects Panel > Video Filters > Matte> Widescreen). To adjust the Widescreen effect on the nest, you will need to control-click on the nest in the timeline and choose Open in Viewer, if you double click on it, it will instead several the contents of the nest.
MtD