I actually find that completely psychotic, and I am weirded out at the thought that they would have children and parents doing fatalities on each other. Do we really want to see Cassie Cage shoot her mother and father in the head, and put bubble gum on it? I can say this, if they allow that, they will get a shit storm of negative press when some psychotic kid murders their parents.
Sindel is also a resurrected hell witch from a fantasy land called outworld. It's easier to suspend your disbelief when dealing with the Sindel Kitana relationship. We, the audience, are supposed to relate to the Earthrealm warriors. They are human. They come from America. They look like regular people.
The whole Cage and Sonya thing will be fucked up from now on as well. Are they married? Even still, we know they have a kid together, so when Cage beats the shit out of his wife/baby momma, and brutally murders her it's kinda weird.