Hi DDKMD,
Do you have a Time Machine backup of your older MacBook? If so, the movies that were downloaded should be backed up. But as a precaution, I would copy all of the movies from your old MacBook onto an external drive before making any changes.
Can you change the settings for your work related movies so that they are downloaded to the new MacBook or to the external drive in the future?
Once you have the files backed up, you can turn iCloud Photo Library off on your old MacBook Computer. The video files will still be available to your new MacBook Pro. Once iCloud Photo library is turned off on your old MacBook, you can delete the video files that you no longer want on that computer.
Get help with your iCloud Photo Library
https://support.apple.com/en-us/HT204570
To turn off iCloud Photo Library for a single iOS device, go to Settings > iCloud > Photos and turn off iCloud Photo Library.
To turn off iCloud Photo Library for a single Mac, go to System Preferences > iCloud > Options next to Photos, then deselect iCloud Photo Library.
If you have Optimize Storage turned on, you might not have all of your original photos and videos on your device. To download the original photos and videos on your iOS device, go to Settings > iCloud > Photos and select Download and Keep Originals. On your Mac, open Photos, choose Photos > Preferences, then select Download Originals to this Mac. Then you can turn iCloud Photo Library off. You can also select the photos and videos that you want to download from iCloud.com.
iCloud Photo Library FAQ
https://support.apple.com/en-us/HT204264
Take care,