1. You can set pin to bidirectional-resistive pull up, but the internal resistor is ~10k and not enough to comply with timing requirements. So there is external 5k resistor required. I believe it is still possible to cheat and not use external resistor by ganging 2 pins together, so effective pull-up resistor becomes ~5k.
2. You shoul read 1-wire protocol, I believe it is more complicated than that. As an example take a look on DS18B20 1-wire communication in this custom component