If the Play:5s are in a stereo pair, separate them in the app then add them as surrounds

Note, PLAY:5 Gen 1s can not be used as surround speakers. It requires Gen 2 or later. 

Follow these steps to add the Play:5s as surrounds:

https://support.sonos.com/s/article/2927?language=en_US

Thank I made the connection, but I think play 5 is too powerful for arc to be surround. Because all I can hear is play 5 not arc 

If you have an iPhone try using Trueplay which will balance the sound between your ARC and Play:5s.

There is also the option in the Sonos app ‘Surround Audio’ where you can reduce the ‘TV Level’. This should result in you being able to hear more from the ARC in your setup.