To me, the satire here (and what the passage says about the Grangerfords) has to do with Twain's attitude towards the Antebellum (pre-Civil War) South and its culture.
By having all this ornate stuff in their home, the Grangerfords show that they buy into the idea that the Southern white elite is an aristocracy. Specifically, they are an aristocracy that is into the values of "romanticism."
Twain thinks this is a bunch of foolishness and that it led the South into many of its problems. He thinks, for example, that this helped entrench the slave society and lead to the Civil War.
The Grangerfords are people of wealth and affluence. Huck is amazed by the house. He describes Mr. Granger as being well born and compares that to being as important for a man as a pedigree is for a horse.
Huck describes the house as the nicest he has ever seen in the country. The door knob is made from brass and the parlor does not have a bed in but a big fireplace. It is bricked on the bottom and kept clean. It is ornate with a clock on the mantel. Two large outlandish parrots decorate each side of the clock.
There is a table in the room piled high with beautiful fruit. They were not real fruit though. The house is also very patriotic with a table cloth that has an eagle on it. There are books. The walls have pictures of the Washingtons, Lafayettes and other battles. There is also a signed copy of the "Declaration."
On of the significant things that Huck notices are the poems and crayon drawings around the room from a deceased daughter of the Grangerfords. They were made by a girl named Emmeline. She had a good sense of humor and seemed comfortable writing about people that had gone to the graveyard. Each time a man or woman died, the girl would create a tribute to them. The Grangerford's had kept her room just like it had been when she was alive.
The furnishings demonstrate that the family are aristocrats and have it pretty easy compared to the life Huck has ever known. They are also politically minded people who are still mourning the loss of their daughter.