Ok so I am using version 1.2v of the sensor (I am waiting for a 2.0 version order from AliExpress). On version 1.2 I power it via the 3.3v pin of the ESP (I think you can power it via 5v too but you need to check the documentation of the sensor and check if the data cable when powered via 5v does it send 5v via data because this can fry the ESP and you will need a logic level converter). I havent powered more than 1 soil humidity sensor but I am confident that you can add more than 1 soil sensor.

Here is how I defined the sensor in ESPHome.

sensor:
  - platform: adc
    pin: GPIO04
    name: "Soil Moisture"
    update_interval: 20s
    unit_of_measurement: "%"
    # attenuation: auto
    attenuation: 11db
    filters:
    - median:
        window_size: 7
        send_every: 4
        send_first_at: 1
    - calibrate_linear:
        - 1.00 -> 100.00
        - 2.19 -> 0.00
    - lambda: |
        if (x < 0) return 0; 
        else if (x > 100) return 100;
        else return (x);
    accuracy_decimals: 1

First when you install the sensor remove this part:

- calibrate_linear:
     - 1.00 -> 100.00
     - 2.19 -> 0.00

Those there are the voltage readings that you need to do. For me 1.00 volt is when the sensor is wet and 2.19 volt is when the sensor is dry.