How do you know your sisters on her period? Your dad's cock tastes like blood
Why would you joke about a situation like that?
It's just a joke, people.
Even when it's meant in jest, a joke like this implies that the harm that children suffer in abusive families is somehow not serious, and that can cause distress for people who have been traumatized.  Besides, think about the impression that you are giving off if someone were to actually believe what you are saying.