"The dilemma was profound," says Pete. "We had to think long and hard and talk very honestly about it. My main worry was for Christina, as I think it's tougher on her. She faces years of bringing up our children alone."
With a calm resolve that has astonished friends and family, they decided to live as far as possible in the present.
"I knew from research that the average survival time was about five years", says Pete. "My days were numbered but I wanted to make the best of all the time left I had."
This week, the writer A A Gill revealed that his cancer diagnosis had prompted him to propose to his partner of 23 years, Nicola Formby.
Pete also decided to ask Christina to marry him, two months after they learned he was ill. "We had been together a long time", Christina says, "and having just been through the worst few weeks of our lives I felt absolutely committed to Pete. There was no way I was going to leave him." He says he would have felt exactly the same if it had been the other way around.
They married in 2010, and decided to start trying for a baby, hoping that his low grade tumour would remain benign long enough for them to enjoy family life. "I understand that some people may think it's selfish to bring children into the world knowing they're not going to have a father", says Christina, "but people have brought up children in all sorts of bizarre situations. It's not ideal when there is only one parent, but the important thing is that you give a child security and all the love you can."
In 2012, Christina suffered a miscarriage at three months but Bella was born in 2014 - joyous proof that they were right not to let the uncertain future rob them of parenthood. Pete was there at the birth. "I think I was in tears before we arrived at hospital. I felt that even though my life was ending, another was starting right in front of me."
There was an interlude of near-normal family life. With enormous support from his employer, Pete, 33, continued to work as a project manager at Royal Bank of Scotland and after a year's maternity leave Christina, also 33, returned to her job as head of strategy at London and Partners, the promotional company for London.
But in April last year, a scan revealed that Pete's grade two tumour had turned aggressively cancerous. It was now a grade four glioblastoma multiforma (GBM) and he was given a prognosis of 12 to 15 months.
"There are always variations but the odds are pretty rubbish," he says. "According to The Brain Tumour Charity, 60 per cent of people diagnosed with a high grade brain tumour will die within a year. I was diagnosed over a year ago, so I am in the lucky half."
"As time goes on", says Christina, "you somehow have to find a way to co-exist with the horror and the bizarre and the fact that normal life is going on as well. You've got this very worrying, scary situation but also the day-to-day routine of going shopping and taking the bins out. It is profoundly odd.
"Sometimes I get angry and upset but I've learned that it achieves absolutely nothing. I also learn from Pete, who hasn't got an ounce of self-pity. He is the most brave and reassuring person. He has dealt with this whole situation without drama or self-pity or anger, which is just unbelieveable."
Pete is a volunteer member of The Brain Tumour Charity's research board, and follows medical developments closely even though they are unlikely to benefit him. Brain tumours are the biggest cancer killer of people under 40 but research is gravely underfunded compared with other cancers; there has been little improvement in survival rates since the Seventies.
The sudden deterioration in his condition - leading to surgery, radiotherapy and chemotherapy - has made them more determined than ever to wrest good from bad. Christina is pregnant again. Pete had sperm frozen before starting chemotherapy and she conceived at the first IVF attempt. The baby, a girl, will be born in February.
"I know I won't see her go to university", says Pete. "But I don't have time to sit around feeling sorry for myself. Bella is running around, looking for something to do, a place to go."
They both value having siblings and wanted Bella "to have someone to share things with and play with." The support of both their families - two sets of loving, involved grandparents - persuaded them it would be manageable.
"Bella has brought such a lot of joy, both to me and Pete and our families," says Christina. "I feel it will give me great strength in the future, when I need it most, to know that I absolutely have to keep going to look after our children. I haven't doubted that getting pregnant again was the right decision. Somehow I will be enough for them, because I have to be."
It must be hard-won but there is an air of easy, child-centred normality at their home in Charlton, south-east London.
Astonishingly, Pete says he has rarely been anxious about the time he has left. "I'm just mindful, about it all. I take it day by day, symptom by symptom."
A hands-on "brilliant Dad", he is enjoying precious time with Bella while he feels well. They watch Frozen, her favourite film, and he takes her to nursery. Nevertheless, he suffers profound fatigue and needs to sleep during the day. When they are in the park or walking back home, Bella doesn't notice how slow he has become or when he pauses for breath.
He has set up an email address for his daughter and when he sees interesting things or wants to tell her what she has achieved, he writes to her in what may eventually become a book. He hopes to do the same for his second little girl.
There is no knowing how long this can go on. They feel sure that Pete will be at the birth of his second daughter and that gives them hope. But Christina knows her husband could eventually suffer loss of speech or memory or a change of personality. "Any or all of these things can happen." They are clearly, in different ways, a source of strength to one another and even to those around them.
"Pete has somehow accepted it and just gets on with it", say Christina. "He is mostly concerned with not worrying other people and with supporting me and Bella and the rest of his family. I am so proud of him for how he's coped with something unimaginably hard."
