You can’t watch the Sky channels from Now on your Samsung TV now, not directly tuned in by the Samsung at least.
You can watch them on the Samsung TV’s screen, yes, but only via the YouView box that BT supplied you with.
Which, unless you were with them from before December 2019, they will want back.
But even if you can keep the YouView box, this too will stop displaying the Now channels once you change broadband away from BT.
So yes, you will have to use the Now app on the Samsung TV to view what your Now memberships provide.
Only BT TV subscribers (which implies BT Broadband, though the converse is not the case) with Now memberships taken out via BT can watch the Now channels in the EPG, and then only on their YouView box.
As regards Sky, Now is a subsidiary of Sky. Sky sell broadband and TV packages, and so do Now, though the value propositions are rather different.
Far too much difference to go into here, though. You really need to bone up on the Sky information for potential subscribers that is on the web, and then do the same for Now.
Once you have got some idea of what each offers, come back with anything you still aren’t clear about, and we will see if we can clarify it for you.
To keep viewing the Community in the previous chronological sequence, under ‘My Settings/Preferences/Preference Options, choose ‘Display’ and select Linear, then choose ‘Linear Layout’ and select Oldest First, and finally press Save. Many thanks to redchiz1 for this Also please note that I am just a customer like you, and my advice may well be worth no more than exactly what you paid for it.