How to isolate sensor power and ground lines as simply as possible
The only issue I see is that the power supply voltage provided to your sensors will be about 4.3V rather than 5V. Q1 is connected as a voltage follower, so the emitter voltage will always be lower than the base voltage by \$V_{BE}\$, which is about 0.7V. Also, the "ground" connected to the sensors will be about 0.25V (the \$V_{CESAT}\$ of your transistor) above the ground of the Arduino, which may cause an error in the sensor output voltages.

You could get closer to 5V if you use a PNP transistor for Q1 but you will need a control line that goes to ground for the PNP.

Even better, replace both transistors with MOS transistors, which will allow you to get much closer to 5V and ground at the sensors.