I think you need to explain a little more what you wish to do. In essence you need to understand that a VPN tunnel (whatever encryption) is a private path between 2 points.
So if you wish for another party to use that tunnel, that party needs to connect to one of the end points to then go via the tunnel to the other end point.
So assuming you have your VPN setup to make the remote database visible on a local LAN, you will then have your remote user also connect to that local LAN to then get access to the remote database.
This connection from the remote user to the local LAN, I assume you would also like to be private, as such you will have to create a separate individual VPN from the remote user to the local LAN, and then (the remote user being part of the local LAN) they can reach the remote database (via the established database VPN).
So in effect you will need to manage multiple VPNs (for multiple end-users), if I understand from your post as to what you wish to do. As such you need to look at you Balance router becoming a VPN server for remote users.