I want to share my traumatic past with my BIL
Do you think your BIL will be able to help you deal with your traumatic past? How can he do so?
He would be able to give me advice on how to move forward.
If you believe that, then it does seem like it would be beneficial to talk to him about it.
The I do plan on sharing it with them. I'm also going to let him know he was a horrible person back then.
I feel like you have a complicated relationship with your BIL and I do not fully grasp your intentions on wanting to share your past, but I hope you just be careful with sharing things with him, and see to it that you can fully trust him and if not, you should not share things that you will not be comfortable with him knowing.