When it does happen, we help them create as much distance as possible and generally do everything I mentioned already to protect them from it happening again. You gave too many examples / questions for me to address them all but I think we are more or less on the same page here.
If I heard my relative was sexually abused by another relative, I would do everything in my power to prevent them ever being in the same room again. You don't need any proof to do this unless it's like a parent/child situation in which case I'd call CPS. You don't need hard proof to call CPS either. Allegations should trigger action to protect and serious investigation. What they shouldn't trigger is punishment.
An innocent person in jail or facing life ruining consequences due to a faulty legal system or extrajudicial punishment is a travesty society shouldn't / can't bear.