Russell Hill and Carol Clay's families have criticised the evidence prosecutors were permitted to show jurors, as they expressed devastation and relief at the two verdicts.
The couple went missing while camping together in the Wonnangatta, Victoria's alpine region, in March 2020.
Former airline pilot Greg Lynn was charged with two counts of murder and faced a weeks-long trial at the Supreme Court in Melbourne.
He pleaded not guilty and claimed both deaths were accidental, but admitted burning down the crime scene, as well as moving and destroying the bodies of the two campers.
A jury of 12 deliberated for seven days and returned a split verdict on Tuesday, finding him guilty of Mrs Clay's murder but not guilty of Mr Hill's.
The victims' families said they were "both relieved and devastated" at the verdicts, and noted the possibility of convicting Lynn of manslaughter had been ruled out before jurors were sent away to decide.
"We thank the jury for their verdict of guilty in the murder of Carol Clay. It was an extremely difficult task given that the accused destroyed so much evidence," the joint statement said.
"The verdict of not guilty in relation to the murder of Russell Hill is devastating.
"There was not enough evidence to be sure of how he died."
The relatives said, since there were no eyewitnesses, the prosecution had "an enormous burden of proof".
"The accused was the only person who saw and experienced what happened. He was also the only person who emerged alive," they said.
They thanked the prosecution "wholeheartedly for their diligent effort" in both the trial and pre-trial, and noted some evidence could not be shown to the jury.
"They had an enormous job putting a case together with limited evidence," the families said.
"They fought hard to keep all their evidence allowed in court, so the jury could make an informed decision, but this was not the case."
Months of pre-trial hearings led to some evidence against Lynn being ruled inadmissible, including large parts of his police interview, character evidence on Lynn and secret recordings taken by police.
The two families said they now wanted to put the case behind them, to begin healing and getting on with their lives.
"We are heartbroken at the loss of our loved ones," they said.
"It will take time to absorb the verdicts ... Right now, we ask you to respect our privacy while we do this."
Mr Hill's wife Robyn and daughter Deborah both took the stand during the trial to give evidence, with the former questioned on her husband's affair with Mrs Clay.
She said Mr Hill told her Mrs Clay was his first cousin when they were introduced and thought it was strange the pair would go on walks together during holidays.
Mr Hill admitted his infidelity after a neighbour found out about the affair.
Victoria Police Assistant Commissioner Martin O'Brien praised the two families for their handling of the difficult four years since their loved ones had died.
"Their courage and resilience in the face of their grief, amidst enormous public attention, has been nothing short of extraordinary," he wrote in a statement.
"We will continue to support them in every way possible following this decision."
He also thanked missing persons detectives for their "determination and perseverance" over what had been an "exhaustive and complex investigation".
