Can One Device Stream to Two AirPorts

It is a limitation until airplay2 comes out and you need airplay2 compliant speakers etc.

There are other options. Do a search as you will find you are far from the first person trying to do this. e.g.

Reminder -- the iTunes ability to play to multiple speakers is not AirPlay 2, but is pretty close

https://www.macworld.com/article/2099925/how-to-stream-ios-audio-to-multiple-air play-destinations.html

I cannot play the music from one device through both AirPorts (stereos) at the same time.

There have been rumors for many months about Apple offering a firmware update for the Express to allow this, but so far, nothing. My opinion is that Apple will never do this, but I hope I am wrong.

Ironically, the AppleTV will allow this, but your "speaker" or amplifier will need to have an HDMI input, since that is what the AppleTV will send in the way of audio.

Presently, you can stream a single song to multiple AirPort Express base stations ONLY from a Mac running OS X or macOS. You cannot do the same for any iOS device ... yet.