Best docking station solution for 4 different laptops - D6000 or W19TB

@SpinCon  The WD19TB isn't an option for systems that don't even have a USB-C port.  You can't use a USB-C to USB-A adapter to plug it into those older laptops, or if you do, you won't get any video output.  The WD19 dock family relies on receiving video through DisplayPort Alt Mode, which involves having a native GPU output wired to the USB-C/TB3 port of the attached system, and you can't have native GPU outputs wired to USB-A "regular USB" ports.

The D6000 is able to connect over USB-A because it uses "indirect display" technology called DisplayLink -- not to be confused with DisplayPort.  But while DisplayLink offers some advantages in terms of universality, in that it will indeed work with all of the systems you listed so long as you install the DisplayLink software on them, the way DisplayLink works comes with some drawbacks that can be significant in many use cases.  I wrote about those in detail in the post marked as the answer in this thread.  However, as you may have surmised by now, that type of option is that only docking station that will work across all of the systems you listed.  Your two older systems don't have any sort of traditional docking connector (USB-C/TB3 or an older style underside docking connector), so docks like the D6000 are the only way to go with them.  And with respect to power, even if you connect the D6000 to a system via USB-C, it only supplies 60W of power.  The XPS 15 9570 and 9530 are designed for a 130W power source, and the XPS 15 9500 is as well unless you have a configuration that does NOT include an NVIDIA GPU, in which case it's designed for a 90W power source.  But either way, if you want those systems to perform optimally while connected to that dock, you'll need to keep their power adapters connected as well, otherwise you'll experience slower battery charging and/or performance throttling -- on top of the drawbacks of DisplayLink itself.  And when the D6000 is connected via USB-A, it doesn't provide any power at all because USB-A doesn't support sending power in that direction or carrying anywhere near enough power to run a laptop.

I would also discourage you from running a 27" 4K display and a 24" 1080p display at the same time.  You'll have to use very different display scaling settings on those displays to allow content to appear a reasonable size on each of them, and while Windows supports running multiple scale factors simultaneously, it can only RENDER for one at a time.  The scale factor that Windows uses for rendering is the scale factor of whatever display was primary at the time you logged into your user account.  For any other scale factor in use, Window continues to render at that scale factor and then uses post-render GPU scaling to enlarge or shrink the rendered content to size it appropriately for other displays.  As you might imagine, that does not look as good as rendering for the actual scale factor in use on those other displays -- but Windows doesn't do that.  So the result of mixing scale factors is that any displays using a scale factor other than the one Windows is rendering for will not look as good as they would otherwise.  This comes up a lot with people who for example have a laptop with a 15" 4K display, where they're probably running 200% scaling, and a 24" 1080p display where they're running 100% scaling.  If they try to use those simultaneously, they'll find that one display or the other will look blurrier than it does when used on its own.  What I've just described is the reason why.  And it's why I recommend that people ensure whenever possible that all displays they're using at any given time can use the same scale factor, or at least very close scale factors, because the wider the gap between the "render" scale factor and the display's scale factor, the more noticeable the inferior result will be.