How does MacOS Photos Library store Live Photos?

I know there has been several posts from recent years about this, but none of the answers really addressed my question here.

Goal: To understand how Live Photos are stored so I can effectively back up (currently using Time Machine and SpiderOak with "download and store originals" turned on in iCloud Photo Library settings).

Question: It seems like all images (NOT including the "Live" .mov file) and videos are stored in Photos Library.photoslibrary/masters, which is great, but when I want to find the "Live" part of each .heic file, I wasn't able to find them, and the .heic file doesn't seem to contain the video portion. So far, the closest I've come is by finding .mov files with completely unrelated names under Photos Library.photoslibrary/resources/media/masters/ and it contains a very confusing folder structure and unrelated file names. This folder not only seems to contain the .mov files of the "live" photos, but also other jpeg files with unclear purposes.

Again, I'm simply trying to understand this to have peace of mind that when I back up Photos Library.photoslibrary, all my Live Photos and edits, etc. are backed up. Furthermore, I'd like to be able to use these files (photos + "live" videos) across devices that may not run MacOS.

Any insights?

MacOS Mojave version 10.14.5 iCloud Photos Library: ON (downloading and storing all originals)

For the simply have piece of mind I would recommend Time Machine to more than one destination and rotating one of the drives off site.

You can have multiple destinations, so get three drives. A, B and C.

Set up A and when the first backup completes remove it and add B and C as dual destinations. Ship A off for a week or a month. If you’re paranoid, ship B away and when it’s safe, bring back A and add it and remove B from the destinations.

Continue the cycle - you’ll have equal data usage and could even leave one drive offline so that for one week, all the backups go to that drive, then swap next week to the other on site and do the offsite rotation once a month.

Every 14 days, you’ll get a reminder to reconnect missing drives if you don’t remove them as a destination.

If three drives or offsite backup is too much cost or hassle, simplify as your needs dictate.