Use of a vault open on different devices at the same time

[Michael]

Let’s have a look from you perspective only.
But it’s the same for your sons pc etc

If you have all vault files synced to your pc ( yours, your sons, etc) you have actually all vaults on your pc and can access them if you have the passwords. (Means you’ll have multiple vaults in your Cryptomator desktop app)

But there might be conflicts when multiple users work on the same files.

Multiple Locations

We should document this behavior somewhere at some point but working on the encrypted data from multiple locations works the same as if you’d work on unencrypted data from multiple locations. If there is a sync conflict, you’re probably familiar with how most cloud storage services deal with this. They’ll create a conflict file (e.g., by appending a (1) to indicate that there was a conflict) and you have to figure out which file to keep. The same happens on encrypted files. Cryptomator is able…

Please also keep in mind, that you can only connect to one gdrive account with the mobile apps.

So the short answer is: yes (for the desktop application) and no ( for the mobile apps)