Marginalised from the onset, Walt Jr. and Marie dont do much. At all. Walt Jr. goes through a period in which he wants to be called Flynn (for some bizarre reason) and Marie steals and pretends to be buying a house (for some bizarre reason) but aside from that both of them dont do much. They are clearly there to provide tense family dinners but that is pretty much all they do. Maybe this is enough though - those dinners make exceptional TV. They do both get their time to shine in the final season however. Walt Jr. fends off a deranged Walt to protect his mother, and Marie cries painstakingly when Hanks death is confirmed, but in the grand scheme of things they wont go down as memorable characters. They were both pretty pointless.