Create yourself a LogMeIn Free account and add these system to that account for remote access. The client loaded on them will run on startup and tunnel out of the networks to the LogMeIn servers to establish an SSL availability connection. When you log into your account from any browser on another system you use for admin purposes, you'll see which machines are available to access. When you connected to them remotely, the connection is completely secure. Read up on it if you're not sure it's for you. Go to www.logmein.com. They even make a client for iOS devices if you're ever in a pinch and need to fix one of these system remotely from your iPhone or iPad. Slick stuff... and it's trusted.
What I would do is match the ports with the assigned laptop.
For example you assign numbers from 1-20 for the laptops.
The default VNC port is 5900 and then you attach it to the IP number of the laptop (you should also assign static ip addresses to the laptops)
So computer 1 port 5901, computer 2 5902 and so on.
I do this for my job, remote into restaurant computers for IT assistance.
We don't use macs tho, just windows.