@Throned  I'm going to assume that's an XPS 15 9570, but fyi it helps to specify the product line rather than just "9570" since Dell uses the same numbering across multiple model lines.  But if that's true, then that system is a Thunderbolt-capable DisplayPort 1.2/HBR2 system.  When the WD19TB is paired with that type of system, half of the video bandwidth is allocated to the downstream TB3 port at the edge of the dock -- not to be confused with the USB-C port near the HDMI output.  The other half is split across all remaining outputs.  So if you're not using that downstream TB3 port, your displays are having to share only half of the total video bandwidth coming from the system.  The fix is to connect one of your displays to that port, using a USB-C to DP cable/adapter if needed.  This is sort of explained in the WD19TB User Guide on support.dell.com.  Notice that when you look at the table for a TB3 DP 1.2/HBR2 system, all of the dual display setups that involve a 4K 60 Hz display require that one of the displays be using the downstream TB3 port.  The U4919DW's 5120x1440 resolution requires almost the same bandwidth as 4K (3840x2160), so the same requirement applies when using that type of display.

So a few questions?

Yes it the Dell XPS 15

So is the dock capable of running two U4919DWs and one 1440 display in their full res(3 total displays), one U4919DW will be in pbp mode so only 1440 for one side. If my setup is capable; then how I would make the connections based on what you have already answered.

@Throned  The dock would be capable of running two U4919DW displays both at their full 5120x1440 resolution if you wanted to. But whether you want to do that or use only half of one of them with your system, you’ll need to connect one display to the downstream TB3 port (using a USB-C to DisplayPort cable/adapter) and the other one to any other output. It doesn’t matter which one you put where. You just need one of those displays to be on the downstream TB3 port so that you’re splitting the total bandwidth requirements of your overall display setup across all available bandwidth rather than trying to run two of them from only half of the total video bandwidth coming into the dock.

Yes I have one coming off the the thunderbolt port using a usb- cable and everything is now full res on both monitors(LG)! 

Im waiting for my stand to come in before hook up the second U49, but as far a bandwidth I shouldn't have any issues because I should have the bandwith due to it running in PBP mode sharing this computer and another computer.

I will keep you posted.