I think what you're after is a powerline network kit, and if you don't need to extend the wifi this will probably do. However, powerline networking is a "sometimes works" solution, because it depends on the electrical circuitry of the property. Also, before spending any money, it is important to realise that persistent lag problems are usually not down to wireless connections, but to a poor broadband connection between the VM hub and VM network. There's some advice below that you may think is too complicated, but if so get your son to do it - he wants a lag free connection, make him do some of the leg work to get things fixed. No co-operation, no lag free gaming.
1) Connect to the hub by clicking on this link http://192.168.0.1/ That should pull up the log in page for the hub. But don't log in, just click on the link "Check router status" That'll bring up a window with five tabs. Open the Downstream tab. Select all the text (Ctrl-A if using a keyboard), copy it (Ctrl-C), then paste it (Ctrl-V) into a reply here as TEXT not screenshots. Post that, do the same for the Upstream and Network log. You'll get an error message when you post the Network log, just click on "post" a second time. Then we can check for any obvious problems with power, noise or error counts.
2) Setup a BQM over at https://www.thinkbroadband.com/broadband/monitoring/quality that'll show what's going on with your VM connection. Post a LINK to a LIVE, SHARED graph here and we'll see what's happening. Usually needs to run for 24 hours before we can draw reasonable conclusions, but the live graph will continuously update so you can post the link immediately.
