@peonia
But this is a family that relies on their bloodline to hold the throne and the authority, wealth and privilege that comes with it! Even though the cousins were from the mother's side and so not in the line of succession, people would be interested in them.
Just looking at more details on the family and the Queen is godmother to Katherine Somervell (born 23 August 1961) daughter of Diana Bowes-Lyon and niece of Narissa and Katherine. So there was a close relationship to that branch of the family.
I just don't buy that they didn't know.
The Queen Mother knew, the cousins were her brother's children. Nobody else in the royal family (and don't forget she wasn't in the royal family until she married the Duke of York), would have known about them unless she chose to tell them. They would have been her age or older - she was the youngest of ten. Princess Margaret found out which is what brought it all to light but her mother didn't volunteer the information. People didn't talk about such things in those days. She may have thought they were dead, they had siblings who died young and their mother wasn't that old when she died.
It was a sad business but, as has been said, a not unusual one at that time.
I had an uncle who went into a home, I never knew him and he died at 26, long before I arrived on the scene. I doubt it would happen nowadays. People live in sheltered or assisted accommodation if they can; in days gone by they were put in an asylum. The type of asylum depended on what the family could afford.
The actor, Brian Rix, had a daughter with Down's Syndrome and the actress, Valerie Hobson, had a son with the same. Both spent their lives in care homes. President Kennedy had a sister in a home, she had a lobotomy! Times have changed, thank goodness.