I have honestly found RealVNC to be the best one, but understand why you may be using TightVNC. All of the other VNC's are basically a derivative of some version of RealVNC. (Interestingly enough RealVNC has apparently put out a PCI card that lets you remote in without software, so you could theoretically get into the system when the OS is down)
Anyway you may want to assign static IP addresses to each system.
So server 192.168.1.5 (example)
Set static IPs for each computer (192.168.1.10, .11, .12) and so forth
Ensure the software firewall is open for the TightVNC executable
Place each copy of TinyVNC on a seperate port, instead of using port sharing. I.E. Ensure the computer using the LAN IP .10 is not running TightVNC on the same...