Twin sisters died within days of each other after both falling ill with coronavirus.
Eleanor Andrews and sister Eileen, 66, are believed to have contracted the virus at the home they shared together.
The family said the sisters "did everything together".
Eleanor's son Stuart said his mum was the first to show symptoms and died on March 29.
Four days later his aunt Eileen died after being admitted to hospital for treatment.
Stuart, from Abercynon, said: "It doesn't feel real. It's beginning to take its toll on us and it's getting harder every day."
Stuart said Eileen and Eleanor's brother Phillip, 68, who lived with the twins, is now in hospital after also testing positive.
He said: "It's terrible, he was still up and about, he was active and to see him go like this you'd think he was a totally different person.
"You think 'it's not going to happen to me - it's not going to happen to me' because things like this don't happen to us but it does, it does happen.
"Just stay in, because this is the effect of people not staying in, and not listening to the government.
"We don't want to put people through what we are going through."
Stuart's wife Janice said: "It's like we're in a horror film or a nightmare and someone is going to wake us up."
Both sisters had underlying health conditions.
Janice said Eileen deteriorated rapidly while she was being treated in hospital.
She said: "We spoke to her on the telephone at about 8.15pm. She was on oxygen and we couldn't make much out. They rang us at 9.15pm and said she was sat up asking for tea and jelly. Twenty five minutes later she had passed away."
Stuart said they will not be able to give Eleanor and Eileen the funerals they deserve.
Janice said: "It has to be a closed funeral and there is only six allowed with the vicar or reverend.
"There will obviously be no wake, no cars, that's all you can do."
