There is no good solution with AVG network products and mobile devices. The best thing I've come up with is to configure them as standalone workstations, i.e. install AVG Network Edition locally on the notebooks and setup policies locally and set the notebooks to update from the Internet.
As for the other workstations, I doubt you'd be able to get the database communications to work very well over an Internet connection. Possibly a VPN could be used, but even that may not work if NAT comes into play.
One idea might be to setup a VPN from your central AVG Admin server to your remote sites. If they all used the same internal private IP settings you may have to setup several network interfaces on your AVG Admin server and have multiple VPNs running at once. Check out the TheGreenBow VPN Client
as that is a good application for this sort of job.
I think that unless you use a VPN you're going to have client errors and not receive info from the workstations. Let us know how it goes and what you end up doing!