Totally confused by the twists of plot as we near the end of Little Dorrit

Well, Dickens does not make it easy to follow the narrative through to the conclusion of Little Dorrit. At least for me, it is extremely difficult to figure out what the characters are saying to one another in the big confrontation scene that moves, over three or four chapters I think, from the prison to the Clennam house, back to the prison, then back to the house, just in time to watch it crumble (of its own weight and decay?) into a pile of bricks, taking with it Mrs. Clennam and her business manager, Flintwatch. Dickens is not going for clarity here; if he were, the minor characters would be, by this point in the novel, more distinct and more distinguishable from one another (it doesn't help that he switches from using names to using various monikers, such as The Patriarch, which I assume is Mr. Dorrit?). OK, so what does happen? As best as I can discern, the evil Rigaud (he, too, has several names and aliases) tries to extort money from Mrs. Clennam; he has possession of a box w/ various documents that will reveal the secret of Arthur C's parentage. She refuses to pay, goes to the prison and tells all to Little Dorrit, who is standing watch over the dying Arthur Clennam; she doesn't care - nothing can faze her or diminish her love for Arthur. So what is the secret? I get that Arthur is not the son of the woman who raised him - but of what consequence is this? Is he actually Little Dorrit's brother or half-brother? If so, it's a good thing that they did not consummate their love, right? But I'm confused and befuddled by these chapters - w/ a few still to go, which maybe will help clarify things, at least in my foggy mind. Figuring all this out requires a more attentive and patient reading than I can give.Something wrong w/ me? With Dickens? Or maybe these details just don't matter - we get the gist of the story by following the life course of the 2 main characters, Clennam and Amy (Little) Dorrit. Just as these revelations and attempted extortion don't mean a damn to the intrepid LD, maybe they don't mean a damn to us, either.