Connecting 2 monitors to a macbook air early 2015

Hi everyone

I have successfully connected 2 LG monitors to my backbook air (early 2015). I am getting a picture displayed on both which is great however I can't extend the displays accross all 3 dispays i.e the macbook itself and then the 2 monitors. Is that possible? I've connected the monitors with an adaptor which connects to the thunderbolt mac and has 2 hdmi outputs to both the monitors? I have spoken with apple support and they cannot understand why it won't extend. When you go into display settings it only shows the 2 screens there and not the 3 even tho i have pictures on both. Is that expected behaviour? thanks for your time.