Triple Monitors with Dell Dock

Hi all, 

Having an issue trying to run a triple monitor setup; I'm using the WD22TB4 dock plugged into my XPS 15 9530, with 3 BenQ G2420HD monitors, the laptop itself is kept closed so the built-in display is unused whilst connected to the dock. 

The first two display's connect and work fine, the issue is the third monitor remains off with no input detected, googling seems to yield mixed results with some saying only two monitors can be connected and some having success with 3.

I realise I'm using some mixed old/new hardware but can't seem to narrow down where the issue could be. 

All 3 monitors are using HDMI out to the dock, one is plugged into the the HDMI port and the other two are using HDMI>DisplayPort adapter to plug into the other two ports on the dock. 

The USB-C/Thunderbolt output of the dock is connected to the USB-C/Thunderbolt port on the laptop. 

All three display's are recognised in the Windows>Settings>Display menu and both 1 & 3 are set to "Extend desktop to this display", however only display 1 shows the additional space with display 3 showing "No input".

Any direction would be really appreciated;

Can anyone help me to figure out if the integrated GeForce RTX 4070 Laptop GPU can indeed run 3 monitors? 

Should I switch to the DisplayPort outputs on the monitors themselves?

Would removing the third monitor from the dock and running it from another port on the laptop via a USB-C adapter work or is this an unnecessary workaround? I'm led to believe the dock should be able to handle all three monitor connections through it.

Thanks in advance!