With my house the living room PS4 and gaming room PS4 can communicate fine. The issue really is down to which ports are forwarded, which the PS4 can handle as it will check if any of the 4 ports are open and use the first it finds.
You can do one of three things:
1) have a newer router with plenty of memory and a decent CPU (ASUS RT-N66U, anyone?) and a new enough version of UPnP that it's no longer a major security hole and use UPnP. The PS4s will work out which ports they need and request them. Seriously.
2) do the above regardless of the router having a decent CPU and RAM, check which ports were assigned and assign each PS4 a static IP and then forward the ports they requested. This is still a preferable option to using UPnP as a whole.
3) just assign static IPs to each PS4 and assign one port to one and the other port to the other. More or less the same thing #2 does except you're just assigning and hoping it works.
I highly, highly, HIGHLY recommend setting up the static IPs in your router and letting the PS4 use DHCP to grab the IP, as it's bad practice to have the client specify its IP address. You should, at this point, see NAT Type 2 on both systems. The connection type doesn't really matter.
BONUS: if you're using an ASUS RT-N66U or the newer RT-AC66U, install Shibby's Tomato firmware fork. It's fantastic.
Believe it or not, that's your router not giving up the port and basically telling the PS4 it's been taken since it was last used. If you turn off your PS4 and flush the UPnP assignments it should only take one port, again.
