How to chian two External Monitors with Macbook Air 2017 13"
The 2017 MacBook Air does not natively support dual external displays. When you connect a monitor through the mini-DisplayPort, you'll only get a single display. Even when using the splitter - you'll always get a single display mirrored across both monitors.

The 3-in-1 mini-DisplayPort adapter is meant for converting the DisplayPort signal to one of three other signals - but only one at a time!

I would suggest using your existing adapter to connect the HDMI monitor to the MacBook Air using the mini-DisplayPort on the MacBook Air. Then buy a DisplayLink VGA adapter for connecting the VGA monitor to the MacBook Air's USB-port. Note that this display won't have the same performance as the built-in display and the HDMI monitor - so if you're using this for intense gaming applications, you'll probably want a different computer.