All of the parents and older relatives are not seen, only heard, with their voices being obscured to sound almost exactly like the adults on Charlie Brown, their voices are garbled in a way so that none of the words are intelligible.
In an Easter egg for "Comic", showing off a display of record albums in a music store, one of them is for a soundtrack for the TV documentary by the Vince Guaraldi Trio (not to be confused with the 1969 film of the same name)