A middle-aged brother and sister were host and hostess at a party. A youth pointed to them and told someone that the host was his uncle. ‘I think your aunt is a charming person.’ Said the other. ‘That’s not my aunt.’ Said the young man. How come?
You assume 'brother and sister' but in this case it is the brother from one family and a sister from another.
"This is the solution I came up with, and I think it works as well: The host brother got married to a woman who had siblings. At least one of the siblings had children, one of whom is the youth at the party"
Sent in by Renai McLean.
The middle aged brother is the young man's uncle, so the middle aged sister must be his mother
Sent in by Robert Gowland
The brother is a monk, and the sister is a nun (or a matron)
Sent in by Robert Burbidge