Different video capture screen sizes - erreurs

I'm not sure this is my problem, but I'll describe it and hope that my title explains my issue.

I captured video using the same screen size (at least I didn't change any setting at the capture) and inserted the video(s) (fractioned) into another project that I use as a template.  The template project already has a small video that is the first one in the "video/audio" series line in the Chronological view (sorry, I'm in a French version and I don't know what the bottom editing view is called in English).

First issue: I have an object (a filter or mask) that we put over the video(s) and I notice that when I resize this object for the first video, it's too small for the subsequent videos that I copied into the template.

Second more problematic issue: for the videos that I added to the template project, I see the entire screen I captured when I position the red horizontal bar somewhere on the video; however when I select the bar and hold on to it to move it along to see movemetn/change within the video the video screen size changes (the bottom is reduced).  So if I place a caption in this area, when you view the project before publication, it will be cut off.

I understand that in both case thes issues are related to a capture screen size difference between all the videos, so how do I adjust the first video (or all of them so that they are all the same size (the largest sizeof them all)?

Thanks in advance for your help!