OK, let's take a minute here.

1. Don't ever base your speed testing on a wifi connection, doubly so if you're in a densely populated area with lots of wifi networks. Wifi introduces too many other factors that can impact your test results. Always use a wired connection for speed testing.
2. Try completely uninstalling the wifi card driver on the laptops in question, and reinstalling. In Windows 10, press Window+E to open a new explorer window, then right click This PC and choose Manage, then choose Device Manager, then expand the Network Adapters group, right click the Wifi card and choose Uninstall Device. Reboot the computer, go back into the Device Manager, and right click anywhere on the right side of the window and choose Scan for Hardware Changes to reinstall it.
3. Have you tried changing the wifi channels being used? The 2.4GHz network should use channels 1, 6, or 11 with a 20MHz channel width. Also try giving the 5GHz network a different name so you can be sure of connecting directly to it, and see if that helps your issues.

I agree a separate router would be a good plan but using a cheapie travel router won't give you a good experience. And if you do wind up using a separate router then be sure to set your Fios modem to bridge mode.