How to turn multiple MQTT entities into unique device using MQTT autodiscovery?

Hi all,
I’m a newbie in Home Assistant and MQTT. I have some Shelly devices and I’m trying to use MQTT since the current Shelly integration is very slow in answering or doesn’t answer at all with battery powered devices. I also tried ShellyForAss but without luck.

For example I have some Shelly “door and window 2” devices to detect open and close of windows ad doors.
That device has 3 sensors (battery level, lux level and tilt angle) and 2 binary sensors (state open/close and vibration on/off).

In configuration.yaml I defines in this way:

sensor:
  - platform: mqtt
    name: "door_blindata_lux"
    unique_id: "shelly_door_blindata_lux"
    state_topic: "shellies/door_blindata/sensor/lux"
    value_template: '{{ value|round(0) }}'
    qos: 0
    device_class: illuminance
    unit_of_measurement: 'lux'
    
  - platform: mqtt
    name: "door_blindata_battery"
    unique_id: "shelly_door_blindata_battery"
    state_topic: "shellies/door_blindata/sensor/battery"
    value_template: '{{ value|round(0) }}'
    qos: 0
    device_class: battery
    unit_of_measurement: '%'
    icon: mdi:battery

  - platform: mqtt
    name: "door_blindata_tilt"
    unique_id: "shelly_door_blindata_tilt"
    state_topic: "shellies/door_blindata/sensor/tilt"
    value_template: '{{ value|round(0) }}'
    qos: 0
    unit_of_measurement: '°'
    icon: mdi:angle-acute


binary_sensor:
  - platform: mqtt
    state_topic: "shellies/door_blindata/sensor/state"
    name: "door_blindata_state"
    unique_id: "shelly_door_blindata_state"
    payload_on: 'open'
    payload_off: 'close'
    qos: 0
    device_class: door
    
  - platform: mqtt
    state_topic: "shellies/door_blindata/sensor/vibration"
    name: "door_blindata_vibration"
    unique_id: "shelly_door_blindata_vibration"
    payload_on: '1'
    payload_off: '0'
    qos: 0
    device_class: vibration

In dashbord they appared as single entities, so I group them in this way (groups.yaml):

Door Blindata:
  entities:
    - binary_sensor.door_blindata_state
    - binary_sensor.door_blindata_vibration
    - sensor.door_blindata_tilt
    - sensor.door_blindata_lux
    - sensor.door_blindata_battery

In this way I have a single tile in dashboard with all the above sensors and they work correctly if the state change.
But this isn’t what I would like to obtain. I would like that all the sensors would belong to a new device called e.g. “Main Door” and I would like to assign that new device “Main Door” to an already defined area e.g. Living Room.

I already googled a lot, really, but I only found this answer that seems similar to my problem:

https://community.home-assistant.io/t/how-to-turn-mqtt-entity-into-a-device/184451/8

but the only thing I understood is that I’d be really dumb since I do not understand the selected solution. BTW I do not know how to obtain the autodiscovery string.
So, how to use in configuration.yaml or whatever else and the mqtt autodiscovery message to build the device?

Thanks in advance

Did you find an Answer yourself? I’m at the same point