I (26F) don't know how to save my siblings (25F, 15M) from parental neglect and a generally bad situation. How do I proceed without making things worse?

This is a doozy. I'm sorry in advance. Also posting on r/relationships.I (26F) grew up in severe poverty, in a violent home (dad beat mom). I have 6 siblings and I am the third child. I "got out" by getting an education and now live in a city making decent money, way more than my family ever has, but I'm not rich.My parents currently live with my older sister (30F), niece, nephew, little sister (25F), and youngest brother (15M). My little sister is developmentally disabled. My parents are her legal guardians. She has been having seizures for several years and my parents have not been good at getting her to a doctor regularly and finding a suitable treatment for her epilepsy. I think she's been on a couple different medicines, but right now they're giving her CBD gummies and saying it's helping. They take $200 of her $300 SSI payment each month for household expenses because my dad doesn't really work. Part time contract basis mechanic. My older sister is doing her best to support everyone on her waitress pay, but she has issues too (nasty divorce process and a possibly a drug problem).My little brother is doing ok overall, but he's never been to a dentist. He doesn't get access to things that he should. The internet bill at their house is in my name and I pay for it because I wanted my brother and nephew to be able to go to school during the pandemic.My little sister had a bad seizure in her sleep today and bit her tounge pretty bad. I am just fed up, but I don't know what to do. I haven't had a willing conversation with my dad since May 2017 because he beat my mom so bad that she was hospitalized.But I want to call mom and essentially say "y'all need to get your shit together and actually take care of your kids. You have one month to show progress, or I'm calling protective services. Don't talk to me unless it's about how you are improving."I feel so lost. I want to protect my siblings but I'm scared and don't know what to do really. Please give me some advice. Is it ok for me to do this? We all know abuse can escalate when confronted. Me and my siblings spent so much of our lives afraid. My big brother is a cop and still won't stand up to my dad.There are so many layers to this, I've only scratched the surface.TL;DR: Long history of parental neglect. I want to help my little siblings, but I don't know what to do. via /r/relationship_advice https://ift.tt/2HlQHdn