Hello @Gros_rouge
When you want to listen to another device with any multipoint bluetooth device you have to stop the media on the device currently playing, no need to reconnect.
Unfortunately, for your second question it is a general bluetooth issue - the sound worsens when you have the microphone active due to shared channels of use, if you just deactivate the microphone the audio quality will get much better. Alternatively you could connect it via a DAC to your device.
Hope this helped