I suppose you are trying to save on wire with that setup. For the sake of the exercise, you might try wiring them more conventionally - 5v to 5v, signal to signal, and gnd to gnd. You still only use 1 4k7.
There may also be a problem of cable length, compounded when you add more DS18B20, or bad home connection. I have DS18B20s on 3m leads, but I have seen them with 5m.