Do you have a star-setup now?
That could quickly become a problem for I2C.
Must keep wire length (capacitance) as short as possible, ideally not more than 3-5m total.
For the inline sensors you have (image), that means sensor-to-sensor (inline) wiring.
Do you have to use a Mega?
An Uno does not have physical pull up resistors, and it's software pull up can be disabled in setup(). So the Uno can become a true 3.3volt I2C master (no level translator needed).
Leo..