You shouldn't have to alter anything on the router, Dave, but if they won't work any other way, then it may be worth assigning a fixed IP address to the plugs, if your router supports that.
You should never have seen an IP addy for one of your machines beginning with 86, generally, they will start with 192, the most commonly used of the private IP address ranges.
The homeplug is just another computer to the router, talking to the machine connected to its companion. Setting it up should be transparent, though the Amazon reviews on your model do seem a bit mixed. Unfortunately, I've never used plugs and the only brand I know a bit about is Devolo.