"The families are there to identify the bodies and to give information to help in the formal identification of those who cannot be identified" visually, a police spokesman told AFP.
Some of the bodies are to be repatriated to Belgium Thursday, he confirmed.
However, that of the driver is expected to remain as "health analyses have to be carried out" to check if he was suffering from an illness that could have caused the accident.
"That's not something we can do in a day," said the spokesman, who added that all of the 24 people injured have been identified.
Meanwhile, the tunnel where the accident occurred was closed off to traffic as investigations are ongoing, police said.
Forty-six children and four teachers from two Belgian schools were returning to Belgium from a skiing holiday late on Tuesday when their coach slammed into a concrete wall in a motorway tunnel near the southern Swiss town of Sierre.