Kadiza Sultana, 16, and 15-year-olds Shamima Begum and Amira Abase left their homes in February and flew to Istanbul before crossing into Syria.
Two of the trio have been in touch with their families to say they have married men in ceremonies approved by IS and are living in and around the Syrian city of Raqqa, the group’s stronghold, the Guardian reported.
The newspaper did not identify which two of the three had got married at the families’ request.
Tasnime Akunjee, who represents the families, told the Guardian that the news had “caused a lot of distress.”
“It entrenches their lives in Syria, rather than in Britain. It erodes significantly hopes that they will come back,” he added.
The paper reported that the two teenagers were given a “catalogue” of men to choose from and that their husbands were in their 20s.
All three of the girls attended the same school in east London, Bethnal Green Academy.
They are believed to have followed a classmate who left a few months previously.
Four other girls from the same school have been given a court order banning them from travelling abroad over fears they too could go to Syria.
The girls’ families have accused police of failing to communicate information which could have alerted them to the risk that their daughters would travel to Syria.
Scotland Yard believes around 600 Britons have travelled to Syria and Iraq since the conflict began though about half are believed to have returned to Britain. -AFP