Have you staffed this with your supervisor at all? This is something that you would want to talk about because unfortunately your job and your personal life got mixed together. You are a mandated reported during and outside of office hours.
When filing a report like this, people always look for a scapegoat as to who is responsible. You did not abuse those children, unfortunately, this family did. They are responsible for their actions, they are just angry because they are now facing real consequences for their actions. People will often look to others to blame for their situation when really they are the ones who created it.
Your sister could have made the report, I wonder why she chose not to? Why is she living in a place where abuse is going on and at what point did she feel it was not her responsibility to call it in? Social worker or not, people should call in abuse when they see it!
Unfortunately as social workers we have to make really tough decisions and people get very angry at us for those decisions. You could very well have saved the lives of those children and even though it is very ugly right now, you did what you had to do. It's not just your mandate, it's your social responsibility to help ensure children in the community are safe.
You cannot control how people react. I have seen people accuse everything and everyone that it was them who made the report. You could also tell the family you made the report if you feel so inclined and explain why you did so. But again, they want a scapegoat. CPS got involved for a reason and they don't want to own the responsibility.
At the end of the day, you did what you had to do. People will be angry and that's okay. They are allowed to feel however they want. That family is now going to get services it needs.