You still haven’t answered what you mean by simultaneously except in the most literal meaning which you’ve already been told isn’t possible.
It isn’t possible to range two two devices at exactly the same time. You can however range to two different devices one after the other. How long after depends on the exact protocol used but can be a very short time period. If these two measurements are taken close enough together than you can treat them as if they were performed simultaneously. How long “close enough” is in terms of time depends on the accuracy needed and the speed at which things are moving.
So when you say simultaneously how long a time period can your application cope with between two measurements to still treat them as being effectively simultaneous?
For example my initial system measured range to 8 anchors. It took 10 ms to make all of these measurements. For stationary or slow moving objects assuming these measurements were simultaneous worked fine. Once I started driving at 30 mph the resulting path would show a speed dependent offset from the correct location depending on when each measurement was last updated. So if all I wanted to track was a person walking I could consider the measurements to be simultaneous even through they technically weren’t. For higher speed objects while it still worked the accuracy decreased significantly due to the simultaneous measurement assumption no longer being effectively true.
As to whether a specific application like jLinkRttViewer can display the results is a different matter. No display application or even device firmware will expose every possible capability of the radio. That is why they supply drivers, source code and documentation, so you can create your own application and firmware to do exactly what you want. The supplied system is indented as a basic demonstration platform not an end product, you may well have to modify some code to get the functionality you want.
On question 2, Yes this is possible with the correct firmware. See previous comments on the potential need to modify software/firmware. The further you get from a simple point to point demo application the more likely you’re going to need to start changing things.
On question 3, see previous comments on “simultaneous”. Only one DWM can talk to one iphone at a given time. But you can cycle through these possible combinations fairly quickly. So how long a time period can you cope with before you can’t consider it simultaneous? This is entirely dependent on your application and how fast you expect things to be moving.