Hello Shanectech: I believe this is your introductory post here on PC. So... welcome to PsychCentral!
I hope you find PC to be of benefit.
I'm sorry you are dealing with this most difficult situation.
Unfortunately I don't know as I have any really creative suggestions for you as to how to deal with all of this. My thinking would be that working through all of this, in-depth & over a period of time, with the help of a skilled therapist may be the first thing you'll need to do.
From my perspective, until you can come to grips with all of this in your own mind I doubt you're going to be able to successfully handle it with your brother. As you wrote, when your brother came out to you regarding the abuse his suffered you questioned it & he shut you out. So you're already "behind the eight ball" on this, so to speak. Plus you mentioned your brother can be violent. So that is another serious consideration.
I don't know if there will ever be a point at which it is going to be workable for you to discuss, with your brother, all that has gone on to say nothing of your brother's boys. That, I think, is part of what you're going to need to figure out in therapy. However given time, & with the help of a skilled therapist, I believe you can come to some resolution in your own mind that will allow you to put all of this to rest & leave it behind.
Should you decide to pursue therapy (assuming you're not already involved with it) one thing to keep in mind is that not every therapist works well with every client. Sometimes it can take a few tries to find the right therapist for you. So it's important not to become discouraged if the first or even the second or third therapist you see doesn't seem to be a good fit. Here are links to 7 articles, from PsychCentral's archives, on the subject of how to find the right therapist for you:
https://psychcentral.com/blog/how-do...dium=popular17
https://psychcentral.com/lib/how-to-...dium=popular17
https://psychcentral.com/blog/10-way...ood-therapist/
https://psychcentral.com/blog/more-o...first-contact/
https://psychcentral.com/find-therapist/
https://psychcentral.com/lib/how-to-...apist-for-you/
https://psychcentral.com/find-help/
And then here are links to three articles related to the topic of healing from childhood sexual abuse; the third being a listing of related resources:
https://psychcentral.com/sexual-abuse/
https://pro.psychcentral.com/recover...-sexual-abuse/
https://psychcentral.com/resources/A...upport_Groups/
My best wishes to you...
