Hello @Soplanpan, welcome to the Sonos Community!
I am sorry to hear you are experiencing issues with the volume of Amazon Alexa on your Sonos system.
1- when asking something, the response comes very, very loud. We have tried to set the volume on the app (both Sonos and Alexa) but it makes no difference. We have also tried to set up the volume with the buttons and then ask Alexa to remember that volume as our preferred volume, but nothing works. Not nice for either us or the neighbours.
The volume of Amazon Alexa should be the same as the volume of the speaker.
We have identified an issue where Alexa sounds louder, no matter the volume of the speaker and are currently working on a fix but I do not have an ETA to share for it.
2- when playing the radio or music (doesn't matter through which platform) and we ask Alexa to turn the volume up or down, it goes up way to loud or way to low. Tried to change the command to "turn the volume up by 1" but it doesn't work.
The increments of volume for Amazon Alexa go from 1 to 10. Number 1 is 10% → number 10 is 100% . You can find more details in regards to the available commands on the following Amazon Support Article Alexa Skills.
We also use a Google speaker and never had that issue with volume control. Unfortunately, we don't seem able to switch to Google voice control.
While it is not possible to have both Amazon Alexa and Google Assistant in a Sonos speaker, you are able to have Amazon Alexa and Sonos Voice Control.
I would suggest to give Sonos Voice Control a chance, as it provides better volume control among other things. For more details, please check our List of voice requests for Sonos Voice Control.
I hope this helps.