Anne was as bright-eyed as she'd been in the 40-odd years that I'd known her although a bit vague and seemingly not quite sure who she was talking with. Georgia explained, sotto voce, that her mother was showing signs of dementia. We commiserated and soon afterwards went to look for our allocated seats in the marquee.

In the two and half years since that interlude overlooking Sydney's gorgeous harbour with its unparalleled view of our national icon, the Sydney Opera House, Anne Deveson was officially diagnosed with Alzheimer's, like her mother and her grandmother before her, and before long needed care which was undertaken daily by her daughter. Then earlier this year Georgia herself was struck down by a brain tumour that was removed but then returned.

We know how this story ends: daughter and mother dying within three days of each other a week ago, a stunning coda to a saga of such sadness that is seems almost unbearable.

Yet while we contemplate the loss, and grieve the going of these two remarkable women, we might also pause to acknowledge the rare gift they both gave us.

Every society needs its truth tellers, to help us see what was not previously obvious, and Anne Deveson and Georgia Blain were among our best.

Mother and daughter both used words to take us to often uncomfortable places. Anne was a journalist in print, radio and television as well as writing several books, including the very tough Tell Me I'm Here (1991) a harrowing account of her son Jonathan's schizophrenia and eventual suicide. Georgia wrote fiction and memoir to explore hard and often unmentionable areas of family life.

They did not write in concert. Sometimes, one was upset by what the other wrote. Tell Me I'm Here was published seven years after her brother's death but it was too soon for her, Georgia told an interviewer. She found it "very distressing". On the other hand, although she consulted Anne about her memoir, she did not give her mother the rights of veto she allowed some friends because "she's a writer herself and she'd written about us".

But, like her mother, she wrote about the once unmentionable: her distaste at being pregnant, her almost crippling fear of the birth and her inability to love her newborn daughter, Odessa. "In about six months I would begin, tentatively, to fall in love. In a year, I would know that love was here to stay," she wrote in her stellar memoir Births Death Marriages (2008). "By the time Odessa turned two, I would feel, without a doubt, that having her was the most miraculous, wonderful aspect of my life."

As her mother had made it possible for families to acknowledge, and start to deal with, schizophrenic children, Georgia spoke for all those women who were too ashamed to admit they were imperfect mothers.

Both mother and daughter also had to find ways to talk about Ellis Blain, the husband and father – and renowned ABC broadcaster – who had made their lives misery.

Georgia dealt by writing about listening to the tape of an interview her father had done with Germaine Greer 30 years earlier. She was embarrassed by his sexism. As her mother described it in a 2004 interview: "… he sounded terribly patronising and he'd say things like …'Tell me Doctor Greer ... do you actually hate men?' And she'd say, 'What a ridiculous question.' … she said something to him and he said, 'Ouch, that's a bit below the belt, isn't it.' And she said, 'If you think I'm the slightest bit interested in what's pattering around beneath your belt, Mr Blain, you're very much mistaken.'"

Georgia said in an interview with Sophie Cunningham in 2008 that Greer had "run rings around" her father and she seemed pleased. She avoided writing directly about the violence of her childhood but her mother, aged 74 when she spoke for more than seven hours to Robin Hughes in 2004 for the Australian Biography interview project, was again ready to say the once unsayable.

"He'd get very angry, and you learnt to get out of the way," she said. "There was a kind of war going on ... and when we did try to get help …I remember we went to ... a psychiatrist, a father of nine ... who ended up telling me that 'your husband is a very creative man, Mrs Blain, and every time he gets into a storm, you must just take the children and leave the house.' And I said, 'Well, what am I going to do? What do you mean, leave the house with three small children?' And he said, 'Well you can sit by the side of the road until it has passed over.'"

Anne Deveson said her husband was angry because she had become more famous and she earned more money yet the family war was hidden from view. After a storm, Blain "would then go and be on air and [be] absolutely calm and together" while the perfect family with three perfect little kids would feature in the Australian Women's Weekly.

We still find it hard to speak the truth about mental illness, motherhood and domestic violence but once it was almost impossible.

Thanks to great truth-tellers like Anne Deveson and Georgia Blain, who found the courage to talk about their families, knowing they would be hurt, it is now easier for the rest of us to recognise, and deal with, the pain and violence in our own families.

Twitter: @SummersAnne