I have four devices at home myself and am almost completely certain you can't transfer your currently playing song from a single device to another or multiple devices (i.e., an everywhere group). It just ain't happening. You DO have some semblance of manipulation functions if you have your Alexa app opened (for me on my home PC - I'm not fond of the tinier smartphone apps). At least there you can, in Spotify (if not Amazon Unlimited) direct music to various devices - phones, your kitchen, bedroom or living room Echo, your Ipad, etc.). However, I realize this is far from what you're seeking.
Not unlike the reasoning for using a single ("Echo") wake-word for all my four devices (that is, because what does it matter or why should I care where I am in my home when issuing an Echo command?), I'm now in the habit of telling an Echo to play "Everywhere" when I request a song (to three full-sized Echos, and not my single hi-fi challenged Dot) because if the sound is good enough to be heard at one location, why not automatically enjoy it everywhere?
Perhaps with this post refresh, at some point someone might advise of a software upgrade earmarked to make this a reality (right behind the ability to rename a device to something other than the four basic trigger words of course).