Complex sentence: When they turned 14, after a succession of therapists had tried unsuccessfully to get them to communicate to others, they were sent to separate boarding schools in an attempt to break their isolation and get them to communicate with others.
Split into simpler sentences: When they turned 14, a succession of therapists had tried unsuccessfully to get them to communicate to others. They were sent to separate boarding schools in an attempt to break their isolation and get them to communicate with others.