If two 16 Channel DVR is installed at one site , is it possible to view both 16 ch. DVR through single LAN & Internet connection .

sure, just configure each with different IP and port numbers. If your system is supported by a central management application, you can even monitor both on the same screen. For the monitoring through internet connection, you'll have to configure the router to forward the appropriate port to the appropriate ip.

It kinda depends - depends on your connection, depends on whether you have a router or firewall, depends on whether that router or firewall lets you configure port forwarding.

If your DVR can support to change the port,and your router can support many port forward,that's no problem.

I think most of DVR and Router can support this function now.