Will my Macbook Air be able to handle dual 4k displays?
Short answer - No.

Longer answer, from Everymac…


  *Although Apple only reports that this model can support a single external display up to 2560x1600, Intel reports that this model can simultaneously support two external displays up to 2560x1600 "daisy chained" via Thunderbolt 2.


The current top spec Macbook Pro, on the other hand, can support 2 external monitors at 4k, but only at 24Hz - same source


  *This model supports a simultaneous maximum resolution up to 3840x2160 on two external displays via Thunderbolt 2. Alternately, it can support a single display up to 3840x2160 via Thunderbolt 2 and a single 1080p display at up to 60 Hz, 3840x2160 at 30 Hz, or 4096x2160 at 24 Hz via HDMI.