letourneau and vili fualaau will speak to barbara walters in a 20/20 interview that will air this friday .
letourneau and fualaau started a sexual relationship when she was his sixth-grade teacher and she fell pregnant with his child when he was 13 .
she served a few months in jail and fell pregnant with his second child within weeks ; she was then sent back to prison for seven years .
but a year after her release in 2004 , they married and are still together .
their now - teenage daughters will join them for the interview .