Reading this I am also so incredibly moved. I truly believe abuse is like a virus, and when someone is abused, often as a means of understanding the abuse, they turn the tables and become the aggressor as coping mechanism, but it is truly that they have been poisoned. Then there is another alternative to surviving abuse, and that is to heal, to love, to be among the strongest people on earth and end the cycle. I can see you are someone who is able to end the cycle- who wants to end the cycle, and I can feel your longing to live that truth through loving and protecting a daughter.
I am so devastated for the childhood you had- and for your nieces. I hope they can grow to be strong like you.
I do hope your aunt finds help.