Yes, I would seek out advice from support services in your area who will be familiar with local laws, shelter options, and legal processes. If you're uncomfortable with this, you could maybe speak to them using hypothetical language instead of making direct statements. This is the difference between saying "my family members are being physically abused; what should I do" (a committal statement) and "if someone becomes aware of family members being abused, what should they do" (a hypothetical statement).
Going to a local resource center is sort of a middle-ground option in between maintaining this secret vs. going straight to police.
You are in an extremely difficult position with this. There will be no good answers here. There will only be difficult options. And whatever you do, whatever happens, it's going to be horrible to endure. Remember you are doing the best you can and that the only person in the wrong here is the abuser.