Data Cap Measure

Not a whining message.  Need to understand the cap.

I have three IP Cameras on my network for my daughter's nursery.  There is a data recording device on the network that records 24/7.  The cameras are available through port mapping.  The modem is connected to a wireless router that does the port mapping.

I use no-ip.org to assign an address to my dynamic IP.  My router bridges to the cable modem.  

The devices on the network, including several mounted tablets and portable tablets, connect to the sample.no-ip.org:port address to access the cameras even though they are connected to the same router as the cameras through a bandwidth monitoring (OpenWRT) router.  

OpenWRT is showing 140 Gigabytes of data requested.  A large portion of the bandwidth is just accessing the cameras.  My data consumption measure shows 275 Gigabytes.  It appears that the meter is counting the camera's upstream and my tablets/computers accessing the cameras despite never accessing the Internet.  All the devices share the same public IP, but just because the router is in bridge mode it seems to count the data.  

I wonder wondering if this is the case.  If it is, I can change the network to use the IP of the cameras instead of the sample.no-ip.org address.  This would require me to disable computer isolation, which is something I value to prevent computers from seeing each other on the network.  If this isn't the case then I will need to spend more time understanding the data usage.  I had always suspected using 200 Gigabytes, but never the 550 I am on track to achieve.

Any advice or thoughts would be welcomed.  I do not wish to move to the business class of service since with the exclusion of the cameras would have very limited data usage.