The sensors don't take a lot of current and still work with 3.3V. The Arduino does not have a problem with powering those sensors.
Can you measure the 5V pin ? Is it at least 4.5V ?
Where did you buy the DS18B20 ?
The real ones are okay, but the cheap ones are counterfeit and the cheap "waterproof" ones are only waterproof for a day, or a week.
The most important wire is the GND wire from the Arduino board to the breadboard. Do you have a single core wire that fits ? Or try two wires.
You could add one or more decoupling capacitors on the breadboard at GND and 5V.
How long are the wires ?
Is your final project one long stretch of wire, or a star-configuration around the Arduino board.
With a star-configuration, you can make more than one 1-Wire bus. Even a 1-Wire bus for each DS18B20 is possible. That causes no problem in the sketch.