Let me preface my post by saying, I completely understand how drained and tired you are and I can't imagine how awful your situation is. I'm not sure if you are familiar with the film "Guess Who's Coming to Dinner" there is a quote I'd like to share with you, "...I owe you nothing, if you carried that bag a million miles, you did what you were supposed to do because you brought me into this world, and from that day you owed me everything you could ever do for me..." It's a quote by Sidney Portier, his character was in a position where his father thought that his son owed him his entire life. It has stuck with me for a long time and I think it speaks true for parenthood.

I am also sad that you most likely have almost a full life-time's worth of experience being manipulated and taken advantage of, and by someone whose role is to protect you from things like that. I would never take a threat of suicide lightly, but there is some probability that she is manipulating you. She has had many years of having conversations in her head about how she would handle you finally standing up for yourself and realizing how terrible of a person she has, and is being to you. I don't want to speak bad about your family, I don't know you, but I just want you to be protected because it sounds like you're in a pinch.

I really urge you to find help and guidance from someone, perhaps the authorities, a lawyer or something if you can manage somehow, to guide you. You have a lot to think about and prepare for, especially regarding the safety of your siblings, your OWN health and well-being, and the trials and tribulations that will come with getting yourself away from all of this, which you very desperately need to do.

Being from the US I don't know the law regarding your situation, you might even try x-posting this into /r/legaladvice but if it is even remotely comparable I would start recording everything, discretely, conversation, video, documents, whatever you can get (without putting yourself in any danger) regardless of what you end up doing, it can only help to secure your final decision I think.

I very truly wish you the best of luck, take care, stay safe, god speed.