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
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.