Just group them with the 5.  It’s easy.  There is nothing special about the turntable, it’s just another Music source.

Grouping means they all play the same thing in sync but not in stereo?

You’d have two rooms, the Sonos Five, and the pair of Ones. Both rooms would be in stereo. 

My personal opinion would be to just play on the Ones, better stereo separation, but you should evaluate how it sounds in either configuration.

The two Ones would be Stereo and the Play 5 Would be stereo too and all playing in Sync.  I agree with @Airgetlam though.  It may not sound good but give it a try.  I tried the same in my Cabin adding my Moves along with the 5s and Sub.  Didn’t do much for me at all.

This.
 

Just select the Five’s Line-in as the source for the Ones. If you group the Five with the Ones I think you’ll lose the stereo separation that you’ll have with just the Ones. 
 

The way Sonos works, I believe that you could even put the Five in a different room and have it play something else whilst still listening to the turntable on the Ones. 

I’ve found that the stereo separation in a Sonos Five product to be great, if I’m within 6 inches of the speaker….beyond that, while I recognize it’s in stereo, it all sounds like “mono” to me as I move further away. Which is why I’m suggesting you try. All sound is subjective, what works for me may not be what works for you. Fortunately, Sonos allows this testing in the real world, without much effort.

See what you like. Fight for your right to be the way that you want it. Don’t depend on random people to force their listening styles on you (but me, @bockersjv and @nik9669a are right )

Seriously though...try if for yourself. Two rooms, or one. They’ll all be in sync. And yea, you’ll get slightly (IMHO) better bass from the Five, but it’s not quite the same as having a Sub or Mini Sub. 

thanks for your comments