Dan,
I understand your fear. It is confusing. The good news is that right now you actually have three copies of your holiday images (maybe four if they are still on the memory card). First, they are in the camera roll on your iPad. Second, they are in the Lr Cloud. And third, they are already on the hard drive where your Classic catalog is.
Classic acts like a vacuum and copies down any full resolution files it finds in the cloud when it is synced to Lr CC. By default it puts these images in the Pictures folder, (but you could change the location for future syncs). To find the location of an image on your drive, do a control click on a photo in Lightroom Classic and then chose Reveal in Finder. This will show you where the images were downloaded to. Once you feel secure in knowing they are all there, you can go about deleting the other copies.
Start by deleting the photos in the iPad camera roll. Deleting from the camera roll is a two step process. First you delete them, then you go to the Recently Deleted Album and delete them again.
If you want the holiday images removed from the Cloud you can delete them from Lr on the iPad, or from Classic on your MacBook. You don’t have to worry about the warning message in Lr on the iPad, because the images were downloaded to Classic.
To delete them from the cloud using Classic, go to the All Synced Photos collection in the Library Module and remove them. This deletes them from Lr CC aka the cloud, but not Classic.
I hope that all makes sense.