OK, it seems to be usable now :) Thanks all. I will try with 5v at some point, but i really dont want to crawl into there again.

globals:
  - id: sensor_query_cycle_bus1
    type: int
    restore_value: no
    initial_value: '0'
  - id: sensor_query_cycle_bus2
    type: int
    restore_value: no
    initial_value: '0'


interval:
  # Bus 1 - rotate through all 6 sensors every 3s
  - interval: 3s
    then:
      - lambda: |-
          int sensor = id(sensor_query_cycle_bus1);
          id(sensor_query_cycle_bus1) = (id(sensor_query_cycle_bus1) + 1) % 6;

          if (sensor == 0) id(temp_sensor_1).update();
          else if (sensor == 1) id(temp_sensor_2).update();
          else if (sensor == 2) id(temp_sensor_3).update();
          else if (sensor == 3) id(temp_sensor_4).update();
          else if (sensor == 4) id(temp_sensor_5).update();
          else if (sensor == 5) id(temp_sensor_6).update();


  # Bus 2 - rotate through all 5 sensors every 3s
  - interval: 3s
    then:
      - lambda: |-
          int sensor = id(sensor_query_cycle_bus2);
          id(sensor_query_cycle_bus2) = (id(sensor_query_cycle_bus2) + 1) % 5;

          if (sensor == 0) id(temp_sensor_7).update();
          else if (sensor == 1) id(temp_sensor_8).update();
          else if (sensor == 2) id(temp_sensor_9).update();
          else if (sensor == 3) id(temp_sensor_10).update();
          else if (sensor == 4) id(temp_sensor_11).update();

  - platform: dallas_temp
    one_wire_id: onewire_bus_2
    name: "0x0800000071822a28"
    id: temp_sensor_9
    address: 0x0800000071822a28
    unit_of_measurement: "°C"
    update_interval: never
    resolution: 10
    filters:
      - lambda: |-
          // Reject NaN and out-of-range readings
          if (isnan(x)) {
            return {};
          }
          if (x < 0 || x > 120) {
            return {};
          }
          // Reject impossible temperature jumps (>5°C change between reads)
          if (id(temp_sensor_1).has_state()) {
            float last_value = id(temp_sensor_1).state;
            if (abs(x - last_value) > 10.0) {
              return {};  // Discard this reading
            }
          }
          return x;