State TV broadcaster RaiNews24 said the sole survivor of the flood that ravaged the home with water and mud was the owner, who had just stepped outside to walk the family dogs Saturday when the torrent hit.
News reports said the man at first clung to a tree, then ended up on the roof of a nearby house. He used his cellphone to call for help but it was too late for the others, who included a one-year-old baby, a three-year-old child and a teenager. The victims were from two families who had gathered in the country villa for the weekend.
A man's body was also found on a guardrail along a Palermo-area road after floodwaters swept away his car, Italian news reports said.
Across the island, in the town of Cammarata, near Agrigento, the fire department said its divers were working to recover the bodies of two people swept away while driving on a road near the flooding Saraceno River.
Also in Agrigento province, firefighters rescued 14 people from a hotel in the town of Montevago, which was threatened by floodwaters from the Belice River.
Agrigento, famed for the ruins of ancient Greek temples, is a popular tourist destination.
Elsewhere in Sicily, at least two other people were missing Sunday after floodwaters swept away their cars, including a doctor heading to the hospital in the hill town of Corleone.
Other storms had battered northern Italy earlier in the week, killing at least 15 people, uprooting millions of trees near Alpine valleys and leaving several Italian villages without electricity or road access for days.
In Casteldaccia, the hamlet where the river flooded the home in Sicily, neighbor Maria Concetta Alfano said she, her husband and their adult disabled daughter fled after barking dogs drew their attention to the rising waters in the Milicia River, the Italian news agency ANSA said. It quoted the husband, Andrea Cardenale, as saying he drove away as "water was up to the hood of the car."
Rescuers retrieved the bodies from the home. A Sicilian prosecutor opened an investigation to determine if any human error, such as possible inadequate drainage of the river, might have played a role in the deaths.