Have you tried the "ok google broadcast" feature yet? After having two Google Home's in our house (one mini/one big) we have started to use it as an intercom. Michelle was sick and with the mini on her night table she could do "ok google broadcast bring me some ice water" - it then makes an attention noise and plays "bring me some ice water" out of the main Google Home. Very handy.

You can also do it from your phone that is linked with your home from anywhere. On my way home I can do ok google broadcast I am on my way home and it will broadcast it out of all the Google homes.