3x PM2.5 + 3x O2 Sensors I2C conflicts

Im trying to do some air quality measurement on an Arduino mega 2560 R3. Im using 3x DFRobot PM2.5 and 3x DFRobot O2 Sensors which use I2C as their communication method. In the code Ive assigned each sensor their own address and I included the code below. Ive hooked up all their SCL and SDA lines to the same 2 pins on the arduino. With this setup I cant get past the .begin() function for the first sensors so Im thinking at this point I may need to just buy the DFRobot Multiplexer to solve this issue but I was under the impression that these sensors if individually addressed can all work on the same SCL and SDA data lines. 

Thoughts ? Thank you in advance!

```
#define Oxygen_IICAddress_0 ADDRESS_0
#define Oxygen_IICAddress_1 ADDRESS_1
#define Oxygen_IICAddress_2 ADDRESS_2

DFRobot_OxygenSensor Oxygen_0;
DFRobot_OxygenSensor Oxygen_1;
DFRobot_OxygenSensor Oxygen_2;

#define AirQuality_IICAddress_0 0x19
#define AirQuality_IICAddress_1 0x20
#define AirQuality_IICAddress_2 0x21

DFRobot_AirQualitySensor AirQualitySensor_0(&Wire ,AirQuality_IICAddress_0);
DFRobot_AirQualitySensor AirQualitySensor_1(&Wire ,AirQuality_IICAddress_1);
DFRobot_AirQualitySensor AirQualitySensor_2(&Wire ,AirQuality_IICAddress_2);

```