Google home to drop in on Alexa??? Is it possible
Not at the present time.
https://www.amazon.com/gp/help/customer/display.html?nodeId=202153130
If the house that has the echo device also has a landline or a VoIP line and you purchase the separate “echo connect” Device which will be available starting December 17, then you could have the Google home call the echo device using regular number calling. But I don’t think the Google home can receive calls, so I don’t think you can go the other way.
I myself am quadriparetic, so totally hands-free phone use is a big deal for me and I pay a lot of attention to the details around the phone calling options. 
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