Unfortunately even though you only have dimmers in a group you can create a scene where a group is turned on at a certain level.
However You can Du it by creating af scene, where trigger could be another scene or the SW on some of your dimmers. It really doesn't matter, cause you Wil never use it
The in Do you just add all your dimmers and set them to turn on at the level you want.
You do that with all the different scenarios.
Afterwards You can hit the "Play" button for the scene to start it.
And you can also create a widget, from where You can start the scene.