"It's just hard, and it only gets harder," said Wylma Cook, the girls' grandmother.
Lyric's father, Dan Morrissey, is awaiting sentencing on several drug and assault charges.
Not having answers about what happened is difficult.
"It's frustrating because you want to know, and you don't get those answers," Drew Collins said.
Evansdale Police Chief Kent Smock said he shares the frustration that there has been little progress to report in the case.
"I've never run into a case like this where there is just so little evidence that we found at the scene," he said. "This case has taken so many different twists and turns as we've followed up on it."
In general, missing person cases are difficult to solve, said Robert Lowery, senior executive director of the Missing Children Division of the National Center for Missing and Exploited Children.
"There is an absence of facts and information that law enforcement has to work through," he said.
Smock said investigators are actively working to solve the case. Authorities are also trying to determine whether Michael Klunder could be connected to the abduction of Collins and Cook.
Police say Klunder kidnapped 15-year-old Kathlynn Shepard and her 12-year-old friend on in May in Dayton. The younger girl escaped, but Shepard was killed and Klunder later hanged himself.
Information from: The Des Moines Register, http://www.desmoinesregister.com