Jeff Coen's book "Family Secrets" covers it all pretty well.

According to Nick Calabrese, the brothers were summoned to a Bensenville, Illinois house on the pretext of seeing Michael inducted, and led to the basement. They were both then bludgeoned to death. Brutal enough, in any case.

On the subject of whether or not the brothers were buried alive, I think it was a suggestion in the initial autospy report that the Feds speculated on. Later reports seem to have concluded that were, in fact, very dead. I may be wrong, but I dont think Ive come across any other reports other than initial one being cited and repeated.

Of course, Nick Calabrese also helped kill some 18 men. Although the state painted Calbrese as a man held in sway by his brother Frank like some sort of LCN prisoner (though by all accounts other than his own, Frank was a mean and nasty a-hole) ultimately Nick Calabrese helped kill a bunch of dudes.

He took down Little Jimmy Marcello and his brother Frank to name a few though. And if it weren't for Pat Spilotro continuing to ask questions, and Nick Calabrese's latter day testimony, nobody would have really cared about Spilotro's murder. Remember Al Tocco had already been "pinned" as a participant in the murder, amongst a litany of other things, by his wife as far back as thew 90's.