I2C interference SENSOR(SCL+SDA) and MasterSlave comm
The Adafruit BMP280 library uses the Wire library. It calls begin() at default pins (D1, D2). And then you begin() the same Wire object at different pins. From that moment the BMP280 library can't communicate with the sensor.

The I2C (a.k.a. TwoWire or Wire) is a bus. Many devices can be wired to the same pair of pins. They must listen on different addresses. So wire both devices to the D1, D2 and use in slave Arduino an address different then the address of the sensor.

The esp8266 and the sensor are 3.3 V devices. The Uno is a 5 V device. You should use logic level conversion on SDA/SCL to Uno.