On question 2:
The DW1000 has no real processing capability, it’s basically a radio which can very accurately time stamp transmission and reception times. The libraries configure it, tell it what data packet to send, read the data packets received, read the packet times and do all of the distance and position calculations.
All the information on how to do that is in the DW1000 datasheet/user manual so in theory you could write your own library and not be limited to how decawave has done things but that’s a lot of work.
I’ll leave BLE and DWM1001 specific questions to those more familiar with them.