I am sorry you were abused and you are struggling like this. It isn't so bad that you talk through things that happened as you are putting your trauma into words. Part of this articuating is "I cannot believe this happened to me", you are at a point where you feel you need to talk it through, that is not a bad thing. Remembering isn't a bad thing, acknowledge what happened, but also make sure you remind yourself that whatever you are remembering is not happening "now" and that now you are safe.
It sounds like you are sensitive and with your brother and sister coming back into your life under bad circumstances makes you fearful and you did not quite know how to handle it, that can be a trigger as often when someone is traumatized, they don't know what to do in the moment. You "do" need to slowly realize that you can get through uncomfortable situations, also that you can protect your boundaries and most likely that is something you are very sensitive to so that when others don't respect your boundaries you probably are reminded of the traumas. Yes, this can lead to struggling with night mares because our brain tries to process and file when we sleep. The brain during sleep doesn't know what to do with trauma, it's gets better as a person gets therapy to talk things out with a therapist who understands trauma.
I am not a professional so I can't diagnose you, however, I do struggle with PTSD myself and have experienced similar challenges and have found that talking things out is helpful because I am slowly articulating the emotional trauma that was storred in my amygdala that I have not put into words as that takes time to do. Most people don't understand that, that when someone is triggered it can bring out emotional challenges that are attached to the trauma that take time to slowly identify with the story of the trauma. However, often when a trauma takes place a person can "freeze" too so they don't always "feel" right away, these feelings, including fears need to be worked through "slowly", it's a grieving process that takes time.