Is it possible to airplay content from iPhone to another iPhone or iPad?
There is one way that I personally know of, and that is using Rogue Amoeba's Airfoil for Mac/Windows and Airfoil Satellite for iOS ($29 USD).

How to send between two iOS devices is outlined in this article (from 2012, but the principle is the same).

Brief version of the article:


You first install Airfoil on your computer, and make it act as an Airplay server.
From the iOS device playing the audio source, you then use the normal iOS AirPlay controls to pass audio to your computer.
You then download Airfoil Satellite from the App store to your second iOS device, and use that application to receive audio from your computer. You just need to assign the Satellite app as a "client" and it will stream audio as usual.


If you are thinking of streaming audio from video sources via this method, then audio will obviously not be synced in real-time with video.

I have however used it for playing video on my iPad and then "taking the audio with with me" on my iPhone. The example would be if I'm watching a TV programme on iPad, and I want to go to the bathroom and continue listening…