London Euston to Watford Junction train service query

Hi.

We are due to travel to Watford Junction on the 6 July from London Euston, as we are catching the shuttle bus from Watford Junction to the Harry Potter Studios.

I received an email from the Harry Potter Studios, that has a “Plan Your Route” link in it to put me on to the Transport For London website.

When I enter London Euston in the from section and Watford Junction in the to section, I only get shown a train route for West Midlands Trains, and there is no mention on there of a London Overground service (which from what I read did/still does call at Watford Junction, with a journey time of around 50 minutes).

The journey time shown with the West Midlands train is 32 minutes.

I was wondering if someone could answer a couple of questions I have please:

1: If I wanted to travel on a West Midlands train, can I use these like I would use the tube trains, i.e. tap in at the barrier at Euston, and then tap out at Watford Junction, or do these trains need a ticket/E ticket purchased prior to boarding the train?

2: With it not showing London Overground in the list of train travel options on the Transport For London website, I was wondering if someone could tell me if the London Overground trains still run between London Euston and Watford Junction and vice versa?

Thanks.