Does the Alexa Skill support VolumeUp and VolumeDown commands?

Since you mentioned that you have a Raspberry Pi running, have you looked at running Node Red? There is a Node Red pallet for Hubitat and an Alexa pallet that can react based on what you say and even which Alexa you are talking to which gives some room awareness.

In this thread, I have some posts on how I achieved some room awareness.