Is Google aware of this issue? Did you or Xiaomi try to contact Google to find a solution?
I don’t know if it’s possible, but xiaomi could add an option in MI Home app to include/exclude Yeelight devices from Google Assistant.
I have already open a topic in Google Assistant support forum but I had no replies…
https://productforums.google.com/forum/#!topic/websearch/k5dbxO0lWj8
Edit:
There is already a topic here in Yeelight forum for that issue