Adding a video lightbox within a CMS multi-image gallery

Hi there, I’m trying to build a cinematography portfolio. It’s the section that starts with “selected work”. Ultimately, i want each project/ collection item to showcase a gallery (another collection list made of the project’s multi image field) and having the gallery clickable. It should link to the project’s video as a lightbox. For some reason when I try to choose the lightbox settings, the drop down menu only shows the project gallery/multi-image as an option and can’t choose the project’s video url field.
Now i’m guessing this is probably because the image lightbox is nested in a collection list made just of the project’s multi-image/gallery and so it’s locked from the parent list.
Is there anyway I can achieve the desired goal? logically i think it should work but after a lot of troubleshooting I can’t find a way.
Here’s a link, mind the website is still a wip, so please focus just on the part I mentioned.

read only link

Here is my public share link: LINK
(how to access public share link)