Are we covered for that by being in a Rick Steves Tour? Or do we need to apply for that ?
You need to do it before getting on the plane, the tour doesn't do it, but it's quite simple.
https://community.ricksteves.com/travel-forum/england/uk-eta-application-experience
It’s nothing to do with any tour company, the airline, the hotel you stay in, the place you get lunch. It’s down to you.
If you are signed up for a Rick Steves tour, they should have sent you an email about it, with details on how to apply. I received the email a while ago.
...and you can do it literally moments before you leave. Unless one of you served time in a prison, you should be OK.