Assuming the software is installed on each machine, it should be showing, but depending on your system they may all have to join the same Homegroup. On the machine(s) not showing up, right-click the taskbar icon and Verify Subscription.
If that doesn't make it appear,. at least on your online account page, I suggest contacting Technical Support.
I checked your McAfee account based on the email that you registered to this forum. I noticed that you are have a multi-device subscription meaning that you can protect any number of devices. Currently there are three devices active in your package.
If all these devices are connected to the same Network it is possible to see 2 devices apart from the one currently installed on your PC.
To check the status on My Account Online visit https://home.mcafee.com/myaccount