Connect Two Dell 27" 2719H Monitors to Macbook Air 2017
Since you're using the P2719H, it has DisplayPort connectivity.  Instead of converting to HDMI, you should just get a mini DisplayPort to DisplayPort cable (mDP to DP).  

You can't daisy chain and since you only have one Thunderbolt port, you will need to get either (one or the other) of:


Thunderbolt 2 Dock with multiple display outputs
USB Video adapter


However, this a lot you're asking this MacBook Air to do.  Remember, there's no discrete GPU as it's integrated into the CPU.  Video memory is taken from system memory (up to 1.5GB worth).  I wouldn't be surprised if you see a noticeable performance decrease or reduced video capability.