Hi Ambrosia,
Looks like you do indeed have a double router situation. Meaning that in the modem that needs to be set to allow passthrough of the IP or disable the NAT function completely making it just a modem.
Once this is done you may have to reboot all boxes..
The static IP is within the Motorola, and will be set to an ip there. When they talk about static IPs with routers they mean in the LAN (Local Area Network) not the WAN (Wide Area Network) address that you get from your cable provider. So you can indeed set static IPs for each machine and I highly recommend this for you with so many PCs on the LAN network.
Getting the info you need is pretty easy.. and Im going to suggest you read this page to help you understand what that information is and how to get it.
https://www.winmxworld.com/tutorials/routers_info.htmlThere is also a link on that page that explains in more detail LAN and WAN and some definitions if you are bothered to read more about all this, but the first link will be most helpful in actual set up for you.
Your Motorola is on portforward.com the site we use most for online guides..
http://www.portforward.com/english/routers/port_forwarding/Motorola/VT2442/WinMX.htmIf this is not exactly like your model, then looking through the installation disk may provide a user manula.pdf this can be very helpful in showing you want needs done. For that matter if you have one for you modem then finding how to disable NAT can be much easier then hunt and peck..lol
Something to keep in mind here is that each seperate machine running winmx will need to have its own set of ports. So you may have to forward in the Motorola a total of 7 ports. A set of two for each of the three computers that run MX, and one for your computer you host from.