yes report anonymously.
Find a new job and encourage your sister to, then just quit, if you want to.
You can say that it's not working out for you (true).
I'd tell your sister you were quitting and it has nothing to do with her, it is not her fault etc.
Why should your sister stop you from leaving. If she has a contract he cannot fire her because you left. And even if he does, there must be another job that would be better for her, she might even get food poisoning eating in the cafe!
Maybe your sister should be looking for a job that is better and you can leave together.
Re "I almost walked out today but after texting my father and getting the response I did, I was too scared to leave. Have a very on off relationship with him and don't want to fall out irreparably with him as he's very prone to cutting family members off. Feel totally trapped!"
Sorry but in your shoes I would have to do what was right and let the chips fall where they do. Don't text your dad to ask about your job.
If you are old enough to have a child you and a job you don't need to ask your dad's advice. If he does want to cut you off for such a trivial thing, is hanging onto him such a prize? Sorry, he sounds awful. You have a new baby, this should be a fantastic time of your life not one where you fear upsetting a shit boss, upsetting dad (sorry, he just sounds pretty awful) or getting your little sister in trouble!
Life is too short. But if you don't feel like this then report anonymously and hand on until it gets shut down.