Nest was merged into Google's home devices unit in 2018, so it should come as no surprise that users can utilize Google Nest speakers as 'intercoms' just as easily through the Broadcast option.  To begin with, you'll need two or more Nest speakers that aren't running on Do Not Disturb, and you'll need to log in to your Google account.  Since you can speak commands directly to most Nest products, you can start by saying, “Hey Google, broadcast…” and add whatever message you'd like after the word broadcast.