Connection to external DB between Own DBs

You should look at replication rather than connection to external DB. You can configure replication to synchronize objects from the master vault to as many other vaults as needed. Only prerequisite is that the properties in the object type on the master vault also exist in all other vaults and have the same alias.

What if I dont want to store information on a server that has access to the internet? Are there any options to access information on my internal server from the external one only upon request?

If you give us more information about what type of prolems you have on "connection to external DB" part maybe we can help on that end.

https://userguide.m-files.com/user-guide/latest/eng/Connection_to_external_database-1.html here is the guide for it

Replication between vaults work in stages:

1. The master vault creates a replication package. You decide the destination. It may very well be a folder on your local network. It could also be on protected blob storage or similar on the internet.
2. If the receiving vault does not have access the original destination you need to move the package to a place where the receiving vault can access it. You can use a USB drive if you want, or you can use a VPN or a transfer service like Wetransfer.com or any other means suitable in your case.
3. The receiving vault imports the replication package from where ever you made it available to that server.

Obviously, the easiest way to automate this process is to choose a destination to which both servers have access. That way it can run automatically in the background without additional manual or automated processes.

Replication between vaults work in stages:

1. The master vault creates a replication package. You decide the destination. It may very well be a folder on your local network. It could also be on protected blob storage or similar on the internet.
2. If the receiving vault does not have access the original destination you need to move the package to a place where the receiving vault can access it. You can use a USB drive if you want, or you can use a VPN or a transfer service like Wetransfer.com or any other means suitable in your case.
3. The receiving vault imports the replication package from where ever you made it available to that server.

Obviously, the easiest way to automate this process is to choose a destination to which both servers have access. That way it can run automatically in the background without additional manual or automated processes.