A brother allowed his friend to sleep with his younger sister in a cheap hotel in Alor Star while he did the same with the sister's friend in another room during the Christmas holiday.
Their action came to light when their rooms were raided by the Kedah Religious Department (Jaik) on Saturday afternoon, reported Berita Harian.
Investigations showed that both couples had only known each other the day before they were arrested.
Head of the raiding party Md Nasir Md Dali said the they first checked the room occupied by the brother and found him clad only in a pair of jeans while his 22-year-old partner was only wearing a nightgown.
He said the sister was found together with her partner and both admitted that they were not married.
Both men work as fishermen while the women are unemployed.
Md Nasir said the department found it quite shocking for a brother to allow his younger sister to sleep with his friend.
He said another couple was also arrested in another hotel during the operations.