You can open the Photos app and iMovie side by side, and drag your videos directly from the Photos library into iMovie. Or, you can do a File/Export of the videos from the Photos app to your desktop, and drag them into iMovie from there.
If your photos/videos are not showing up in the Photos item in the iMovie media sidebar, possibly that is because your Photos library is not designated as your system photo library. To check, open the Photos app on your laptop, and do a Photos/Preferences and look in General preferences. If the box that says "use as system photo library" is grayed out, that means that it is already designated as the system photo library. If it is not grayed out, click on it to gray it out. Then see if your Photos app videos show up in the iMovie media sidebar photos item.
-- Rich