Missing Stabler Girls

Maureen Stabler, first child of Elliot and Kathy, played by Erin Broderick.
Elizabeth Stabler, fourth child of Elliot and Kathy, played by Patricia Cook.

Both of them haven't been seen since Season 8- four years ago! Maureen was last mentioned in season 10's Lunacy and Elizabeth was last mentioned in season 11's Perverted...even still where are they? Why are the other three children (Kathleen, Richard, and Eli) are getting the glory more often then these two? And Elizabeth is supposed to be Richard's twin sister and still living at home!