How can I make a Furby hate people?

It's possible. Sibling rivalry is real! Just use the tips in this article. They apply to siblings, too.

No.

The advantage here is that you don't have to interact with the other person. So in this case you are the one keeping the hatred alive. Try some of the...

You can use the same instructions listed above. Simply add batteries and reset if it necessary, and you should be good to go.

You could try pressing the reset button inside the battery compartment. Although, the Party Rockerz' reset switch is on the outside, and the 2005 furby has an on/off switch.