I'd just like to say, in response to the suggestion from Jane10 that you post a response to your brother's post on Facebook, to think twice about doing that.
A similar thing happened to me when a cousin we'd all lost touch with found some members of our family on Facebook and put up a long and effusive post about my dead, abusive father.
A niece of mine, with whom this cousin had made friends on Facebook, responded, tagging others of us with whom she was friends on Facebook in a list "father to Nodding, grandad to Nodding's children" etc.
I simply replied politely, asking my name to be taken off the list, together with the names of my children who were born after his demise, as he'd been the worst father in the world as far as I was concerned and I had deliberately not had children until he was six feet under as I had sworn, as a teenager, that he would never have any contact with any children I might have in the future.
I said I did not wish to have my name linked with his on a public forum.
The most awful public row ensued as the niece concerned decided to lecture me on the thread and I was so incensed, I retaliated. These things can turn really nasty when raw feelings are exposed.