Having now looked through this thread, and also followed up some research myself regarding Windows itself being unable to do what you want.
If the last above suggestion from terry1966 is not what you can work with, the only solution is to send the two USB monitors back and obtain monitors with VGA ports.
Providing the laptop does have a VGA out port, you can buy VGA splitters which can provide a lot more than just the two monitors you require, bearing in mind, those with more than two outputs do require to be powered.
Considering that Windows cannot do this in itself, using USB monitors, the VGA route is the only one that can work.
Nev.