Cisco NAT ISP – How to Combine Two ISP IP Addresses into One

This depends on exactly how the ISP provides them to you. You may have "4 DHCP addresses", a "routed" /30, or a "connected" /29.

For example, Time Warner Cable (business class) allows 4 devices to use DHCP to get an address. (similar to residential service that's limited to one)

"routed" is what you'd see where you have a WAN side and LAN side. This is the traditional "lease line" model where the T1/DS3/etc. ISP side has an independent address to which the static address block is routed; from there they can be assigned as a LAN or NAT'd individually (the firewall situation Bulki mentions.)

"connected" would be where the ISP provides your LAN (i.e. a data center, or the "routed" example where you don't control the router)

I’m trying to understand what you’re asking, and based on how you described the network setup, there isn’t any good reason to use private addressing; even if you need to use separate network for other functions. The link you provided in the comments advertises that it handle multiple subnets.

I would start with setting your Draytek Vigor up as a DHCP server that assigns the public address space (84.x.x.*) you have been allotted. This will take away the NAT and allow inbound requests to your public addresses with relative ease.

If you want to keep your private IP address space intact, then you would set up your server (192.168.1.10) as the DMZ for your WAN address (212.x.x.x).