Bridging the wifi networks on nodemcu: how to set the esp8266 as wifi extender, simplest case
The esp8266 will not bridge the networks. You can perhaps bridge the communication from your other ep8266 on the TCP level with WiFiServer and WiFiClient. Send the sensor value to middle esp8266 running AP and it sends the value to Raspberry.

With MQTT you could create some MQTT proxy. Receive the data with WiFiServer and forward it with WiFiClient. without parsing or anything, only copying the chars between servers client and local client in booth directions

something like this (not tested):

void loop() {

  if (!serverClient || !serverClient.connected()) {
    serverClient = server.available();
  }
  if (!serverClient || !serverClient.connected()) {
    if (client.connected()) {
      client.stop();
    }
    return;
  }

  if (!client || !client.connected()) {
    if (!client.connect(raspiIP, MQTT_PORT)) {
      Serial.println("Can't connect to MQTT");
      delay(1000);
      return;
    }
  }

  while (serverClient.available() &gt; 0) {
    client.write(serverClient.read());
  }
  while (client.available() &gt; 0) {
    serverClient.write(client.read());
  }
}