Are you using the S1 or S2 app?

You can add two Fives as surrounds but unless you have a large room, Fives are a bit overkill. Consider adding two One SLs as surrounds instead.

On your Apple TV, be sure you have Change Format turned on and Dolby Digital selected as the Audio Format.

Thanks

There is the older gen.

Sonos Play5 Gen 2 Black

Will these work as surround too ?

Yes, the Play:5 Gen 2 will work as surrounds.

Apologies, I do not understand audio systems much.

Will adding the speakers give me much louder and immersive sound ?

As I understand it, all the speakers will be upfront under the wall mounted TV.

Sub…. Play5     Playbar     Play5

(there will be none at the rear)

or 

Will the Pay 5’s be behind me when I am watching ?

The Play:5s would be added as REAR surround speakers, meaning they will be placed behind where you are seated. You cannot add any more Sonos speakers to the front with your setup.

Adding rear surrounds will give you a more immersive audio experience especially when playing 5.1 content, but it won’t necessarily sound louder.

What type of audio are you currently getting from the Playbar from the Apple TV?

I am using the S2 App

The Audio with the “Playbar” & “Sub (Gen 2)” is quite good. But sometimes not loud enough for me (aint got great hearing). like some Marvel movies on Disney+

My bose, proper home theatre with sub and 5 speakers is much much louder.

What type of audio are you getting from the Playbar when streaming movies from Disney+? While you are playing the movie, the Sonos app will display the type of audio on the Now Playing screen:

Hi,  it says “Stereo PCM” 

I have set its as Dolby in my Apple TV. Still remains “Stereo PCM”.

The HDMI 2.1 cable from the Apple TV is going to my LG TV hdmi ARC port, from the LG TV to Sonos.

*******

I had a really Duh moment. The volume in the Apple TV was set to low. Once I set it to 80% in the Apple TV.  The volume is more than loud enough with SONOS. 

You should be getting Dolby Digital 5.1. What model is your LG?

It is the LG UHD 86_75UK6500PTB

https://www.lg.com/au/support/products/documents/UHD%2086_75UK6500PTB%20Product%20Spec%20Sheet.pdf

Do you mind posting some screenshots of your audio settings?

Settings on TV ?

Yes, the audio/sound settings on your TV.

I will update tomorrow, as people are sleeping. Apologies