“My dad has Parkinson’s and he can’t leave the house,” Williams said.
“He used to sing with me every night on stage, he would come out, steal the show and be charming and then wander backstage for a glass of red wine.
“Now he can’t leave the house.
“My mother-in-law, who I absolutely worship and adore, has three illnesses.
“She’s got lupus, Parkinson’s and cancer. She is the most courageous lady and she is fighting, fighting, fighting.”
He added: “It’s a strange place to be, this place we find ourselves, 51 years old, it’s very strange to be the grown-up.
“I’m not ready for it.”
Williams has previously discussed his mother’s battle with dementia and accepted that the day would arrive when she no longer recognised him.
He said: “I’m in a different part of my life right now.”
Meanwhile, it was reported earlier this month that Williams had been nominated for a knighthood for his services to music and charity.
Williams has had 15 chart-topping albums in the UK and has also won a record-breaking 18 Brit Awards during his career.
Williams was also responsible for the creation of the Soccer Aid charity football match in 2006, which has raised £106 million ($238m) for Unicef.