The two Play:1s are compatible and can be upgraded by adding them to the S2 App in use by the Arc. You can then bond them both as your Home Theatre rear channel surrounds.

The Play: 5 - will depend on which generation you have - A Gen1 is not compatible with S2 and so cannot be used with the S2 App or the Arc but, anything newer can be added to S2 and grouped with all your S2 rooms/speakers which might be useful for playing TV audio in different rooms, or music audio in the same physical room etc.

Also see the link here for S1/S2 App compatibility with all Sonos products:

https://support.sonos.com/en-us/article/sonos-s2-compatibility