Hi. No you don't yet understand how rooms work! But that's soon rectified. 

A "room" is just a label for a speaker, or a set combination of speakers, such as a stereo pair.

Just call the Beam 'Beam' (say).

If you want all the speakers in your (physical) living room to play together, just group them.

A Sonos “room” can either be a single speaker, a stereo pair, or a soundbar (with or without surrounds/sub). Portables are also their own room.

You can clearly have speakers in the same physical room ie. Living Room, but you can’t have a single One and Beam in the same Sonos “room”, hence the need for “Living room 2”.

You can rename the respective Sonos room name to anything you like (assuming the room name isn’t already being used)

Thank you Didn't think I did, hahaha

You could also think of a Sonos room as the smallest entity on which a separate stream can be played.  You could now play audio just on Beam, just on tbe One, the same stream on both or different  streams on the two speakers. (As the two speakers are in the same physical room in this example this last option might not be a good option)

I thought it was going to be like Google Home where you have rooms and then add products to the rooms. All sorted now though, thank you

I actually had a similar issue to yours, but the behavior was different. 

I added a Beam to Master Bedroom where I have a single One located, and while adding the Beam it wouldn’t let me automatically select Master Bedroom (not sure if it’s due to the name being already used, or the “Master” label falling out of favor). However, afterward I was able to “rename” the Beam to “Master Bedroom” and have two “Master Bedrooms” show under System->Products. So no issues with identically named rooms/products there.

I’ve been using Sonos devices for over 10 years, but I guess I’ve never had more than one device in a room at a time that wasn’t a stereo pair. I’m not sure if the current way Sonos is handling this kind of scenario is the best, but I guess I guess the names aren’t ultimately that important unless you’re looking to create rooms in a virtual assistant. 

During initial setup of the Beam, the app wouldn’t allow you to select Master Bedroom for the Beam as a Beam and single One cannot be in the same Sonos room.

However, I just tried and you can manually rename rooms with identical names.

The Room name is an identifier. If you use Sonos Voice Control (SVC), room names are important when grouping and ungrouping by voice control therefore it makes sense to have unique Sonos room names for your speakers.