Macbook Pro 2017 with 2 thunderbolt ports with triple monitor setup
In order to get this setup working, you'll want to get the following:


2 x Thunderbolt 3 to HDMI cable    
1 x DisplayPort to HDMI adapter-cable   
1 x USB-A to USB-C adapter


You would connect the first monitor directly into the MacBook Pro using the Thunderbolt 3 to HDMI cable.

The second monitor connects to the dock's Thunderbolt 3 connector using the Thunderbolt 3 to HDMI cable.

The third monitor connects to the dock's DisplayPort connector using the DisplayPort to HDMI adapter-cable.

The YubiKey connects to one of the dock's USB ports using the USB-A to USB-C adapter.

Example products:

Thunderbolt 3 to HDMI cable:
https://www.amazon.com/uni-Thunderbolt-Compatible-MacBook-Pixelbook/dp/B075V5JK36

DisplayPort to HDMI adapter-cable:
https://www.amazon.com/AmazonBasics-DisplayPort-HDMI-Cable-Feet/dp/B015OW3M1W

USB-A to USB-C adapter:
https://www.amazon.com/ARKTEK-Adapter-Convert-Samsung-Aluminum/dp/B075R95QM7