to the Question 1: In general, multiple VIN blocks can be used to read quality from multiple sources. Unfortunately, it probably won't work in your case, because all the data comes from one source (REXduino block).
to the Question 2: In REXduino, it is currently not possible to ensure that a 1-wire sensor will always get the same address if there are more sensors. We recommend using Monarco HAT or a 1-Wire hub instead of Arduino.
Using another hardware (with the Raspberry Pi) should also help solve the first problem. In the Raspberry Pi, it would then be possible to fix the addresses of the individual 1-wire sensors using this manual.