An Auckland mum and dad are fighting to stay alive for their sons after they were both struck down by terminal lung cancer, despite neither being a smoker and both living a healthy lifestyle.

Graham and Mery Brooke-Smith began their fight last January when Graham was diagnosed with stage 4 lung cancer that had already spread to his spine.

That tragic news was compounded just months later when Mery was also diagnosed with stage 4 lung cancer, which has been more aggressive and spread to her spine and thigh bone, requiring surgery.

Their two sons, aged 9 and 11, are now facing the possibility of losing both parents — but mum and dad are fighting hard for their boys.

Friends have launched a Givealittle appeal to help the pair, who face crippling bills with only their chemotherapy covered.

The appeal stated that Graham's ongoing treatment will cost his family at least $100,000 and the couple do not have medical insurance.

On top of that, Mery's treatment will cost $90,000 for six months and then $2200 for every subsequent month.

The cause of their cancer remains a mystery, with neither parents smoking and both living a healthy lifestyle.

"Please consider helping to fund their treatments so that their boys can have their Mum and Dad for as long as possible," the Givealittle page asked.

"Your generosity is greatly appreciated."

Graham and Mery Brooke-Smith told Stuff they want to fight their cancer to "at least to see our boys grow a bit older".

"With just chemotherapy, we're looking at two years. With the whole treatment, we can be around for four or more years," Graham said.

He said the couple began drawing up plans when he was first diagnosed, but the cruelty of Mery's diagnosis was a shock.

"That's when I cried, that really hurt because our boys were going to be orphans," he said.

The couple has now arranged for a family friend to care for their children when they die.

"We can't believe that this has happened, at the exact same time for the both of us – it's insane."