A woman and her two sons have died in the space of five days after testing positive for Covid-19.
David Lewis, 81, from Pentre, Rhondda Cynon Taf, lost his wife Gladys, 74, on Thursday last week, and sons Dean, 44, the next day and Darren, 42, on Monday.
All of them lived in the same block of flats in Treorchy. Other family members are now isolating.
Dean's widow, Claire Lewis, said the family were struggling to come to terms with what had happened.
The family, she said, had been careful to avoid catching Covid-19 because Gladys had chronic obstructive pulmonary disease (COPD), Darren, who had Down's syndrome, had been on life support with pneumonia earlier in the year and her husband David "was not well himself".
Mrs Lewis said she did not understand how they had caught the virus.
The 44-year-old, from Treorchy, said: "We are totally devastated, all of us. My father-in-law is broken, he has lost his wife and his two children.
"He keeps on saying to us, 'It should have been me, it should have been me'.
"It's so difficult to try and help him, and hold me and my children together, because my children are absolutely devastated, and my sister-in-law is.
"She just she does not know what to do with herself, she is the baby of the family and she has lost her big brothers."
She said her mother-in-law Gladys would do "anything for anyone".
"To think she is not going to be there anymore is almost heartbreaking," she said.
Mrs Lewis, who has three children, warned people thought Covid-19 was "a big joke".
"People need to wise up," she said.
She added being in isolation made coping "so difficult".
Mrs Lewis and her youngest son, 12, have tested positive for the virus and she is waiting on results for her eldest children, 14 and 19.
"People don't think this is going to happen to them, but look at our family," Mrs Lewis said.
A GoFundMe page has raised more than £5,000 for the family since being started four days ago.