Oh dear OP, I'm so sad for you (and your siblings) about this. :( What a horrible thing to hear.
I wish I could offer more constructive advice. Can you discuss this with your brother? If you can't discuss it with your siblings (assuming they don't want to, I mean), then perhaps you could see a counsellor? I'm guessing your DH is supportive, but out of his depth in terms of helping you "properly" IYKWIM (beyond just supporting you, I mean - sorry not explaining myself well here at all).
Perhaps you could open a conversation with your brother about how he told you that your mum abused you? See where the conversation goes from there?
So sorry this is happening and your siblings can't/won't talk about it. :(
I'm sure people with better practical advice will be along soon.