However, the group doesn’t have the same states as the sensors. the sensors have open/closed whereas the group has on/off. Is there a good way to change it so the group also shows open/closed?
Apologies, I was going for a drive by solution and did not check on your familiarity with HA.
As Tinkerer above points out ALL binary sensosors are just that, they are either ‘on’ or ‘off’
The device class applied to that sensor allows the front end to interpret what ‘on’ means and what ‘off’ means.so that can be presented in the front end.
They are still just on and off.
The way to use device class is (as @KTibow says) add a customisation: customize: key to your configuration (it has to go under the homeassistant: key and indented 2 spaces)
Then just follow the examples in the link I posted above.
The documentation covers all sorts of these golden nuggets
If you include a random selection (given settings) of devices in a group, unless they are the same ‘device class’ you will get what you observed.
You will need to add each of your devices in a similar fashion.
Then when you group them they will all be singing the same tune.
Note: the spacing is important
homeassistant: has no spaces before it
customize: has 2 spaces before it
binary_sensor.whatever has 4 spaces bofore it
device_class: whatever has 6 spaces bofore it