Some answers about the orb

And immediately your "father" finds something interesting.

"The orb of Dragon Dayama is an alleged magical artifact with the power of body swapping by means of transformation. If it is broken, it permanently swaps the bodies of two persons in the room. The voice of the swapped persons stays the same as their original though, unless they concentrate on the voice of their new body!".

"Wait, permanent?" your father in Nina says and then has a sudden idea. "Wait, permanent? Crap, this voice thing really works!" he says first in Nina's, then in his own male voice.

"There is one exception to the permanent part, however. If the transformed person orgasms in their new body, they can temporarily revert to their original body for a short period of time if they chose to!".

Now all three of you exchange glances. Finally you and your "father" settle on Nina.
"Uh, guys... What are you up to?" Nina asks in your father's voice.