I also have a 2017 MacBook Air and it only accepts a single screen hooked up to the Thunderbolt 2 Port. That's also what Apple says the Air supports. I have a 1080p screen hooked up through a minidisplay to HDMI converter cable.
https://support.apple.com/kb/SP753?viewlocale=en_US&locale=nl_NL
Graphics
Video Support
Simultaneously supports full native resolution on the built-in display and up to 3840-by-2160 resolution at 60Hz on an external display, both at millions of colors
- Thunderbolt digital video output
- Native Mini DisplayPort output
- VGA, HDMI, DVI, and dual-link DVI output using adapters (sold separately)
So 2 screens at the same time isn't going to work (only the built in screen and 1 external).