I am an adoptee and one of my major concerns on being contacted by my birth mother was that the hurt and anger I feel about it would spill out at her and drive her away. I didn't want that to happen but I knew it was a strong possibility.
I have read the primal wound. Get it for yourself and your brother and pass it on to your dsis and your mother. It helped me understand a lot of why I am and act the way I do and made me realise the way I feel and act is not unusual and is the way may other adoptees also feel and react.
I would also suggest you, your sister and brother contact Norcap between you and pay for an intermediatory to help you all with contact and working through your/his issues if you are wanting to have any kind of future relationship with each other.
It cost me £150, but my NORCAP intermediatory has been fantastic in helping me on my journey. It has allowed me to express my hurt, frustration and anger without it being directed at my birth mother. It has also allowed her to discuss her feelings, shame, sadness, guilt etc without either of us feeling like we have to hold back from each other. I can also ask the questions I want to (who was my father, what lead to this decision etc) via my intermediatory, without putting her on the spot or it interfering with us getting to know each other. She has kept these feelings buried for a long time after all and is having to work through a lot of issues herself.
Contact has ground to a halt for us. Not because we are angry, but I think it's more us both dealing with our feelings and being ready to move on. More than anything I am scared of being rejected again and putting myself forward into a situation where that could easily happen isn't easy.
Your brother has probably had a lot an anger and hurt within him for years, but, if he's anything like me, was completely unable to express it to his adopted family for fear of being rejected again. Now he can express that anger to some degree it is probably beyond what he even realised and being as you and he had no choice in these decisions, maybe he feels safer in expressing it to you on some level.
However he can't lay all that on you and expect you to be able to deal with it. IMO he needs proper help and to talk with people who know about this kind of thing.
So I too suggest NORCAP for him as an option for dealing with his feelings and working through them. Otherwise he can go to his doctor for councelling, however if he does not get a counceller experienced in adoption they may not understand - as I found when I was a child sent for councelling which seriously backfired and left me unable to talk or trust anyone since.