I think I get it, so it's the track motion button on each track ? (I removed it a long time ago because I though there were too many buttons on my tracks).
Edit : thanks for adding the picture (that's some really nice cows).

Most Vegasusers even don't know that with the Track motion Tool you can also go 3D.

Oh my god it works! So easy now with pan/crop and track motion together... I just have to find a way to make sure the separation between the two videos will be right in the middle of the project frame to make in easier, instead of eyeballing it each time, but even if I can't, sure it will be harder but at least I can enlarge, crop, and move my picture. So great! Thanks everybody and you especially 3point.

Also Is there a way to apply track motion to items and not the whole track in order to avoid dedicating a whole track to each item (box)
Edit : 3D cinematic looking cows, that's greatness itself.

I think I got it pretty well now 😀 😎 😀 : I have to make sure to crop to a 32/9 format in the pan/crop settings, with numbers on the pan/crop settings that are even or correspond to a "standard format" (something like that) in order to avoid stuff like 1 pixel black bars near the frame (because pixels can't be divided).

So I've been looking for 32/9 resolutions (3.5555555... etc... ratio) with even numbers and have found these values that should work well (but I will ultimately I find them all) :

Height 540 ---> Width 1920
Height 306 ---> Width 1088
Height 270 ---> Width 960
Height 252 ---> Width 896
Height 234 ---> Width 832
Height 216 ---> Width 768
Height 198 ---> Width 704
Height 158 ---> Width 560
Height 144 ---> Width 512
Height 108 ---> Width 384
Height 72 ---> Width 256
Height 54 ---> Width 192
Height 36 ---> Width 128

Then to get the separation between the two videos at the right place in the middle, I just have to set the y position on the track motion settings to 270 (for the upper video) and -270 (for the bottom video). 270 is one fourth of 1080. The video is (by default) in the middle of the project frame, so if I move my videos up or down 270 pixels, I'll get it right.

I can even easily add some keyframes in the pan/crop settings with just two clicks and one drag (or even crop change to zoom in and out) in order to focus more on what I want in the frames. Unless I'm mistaken somewhere, I think it's going to be great.

I think I got it pretty well now 😀 😎 😀 : I have to make sure to crop to a 32/9 format in the pan/crop settings, with numbers on the pan/crop settings that are even or correspond to a "standard format" (something like that) in order to avoid stuff like 1 pixel black bars near the frame (because pixels can't be divided).

No need to do that so complicated, just make once a 32:9 crop setting in pan crop tool and save that setting as a preset. Than you can quickly attach that setting to other events.

In track motion you have the possibility to snap to a predefined grid, no need to set manually numbers like -/+270.

Thank you, it's nice that I can save everything. I just tried to use the snapping button in motion track but it only snaps well on the sides, not on the top and bottom where it cuts the image.

Depends on, Track motion snaps with it's center point (you can move that point to a side or corner when needed) to the grid points, how many grid points there are you can also set.

@Marty111 Track motion tutorial ...

Here are a few more goodies for your next project.
While made with an earlier version, the basics are still the same.

http://tale2tell.com/sony-vegas-pro/