The Stepford Cuckoos
The Stepford Cuckoos or The Three-In-One are mutant triplets who are psychically linked to each other and possess tremendous telepathic abilities, along with the ability to change their bodies into diamond-like matter to avoid mind projections or psychic blasts of any sort ( same ability as "Emma Frost / White Queen''). They are Celeste Cuckoo, Esme Cuckoo and Irma Cuckoo. They are students at Xavier's School For Gifted Youngsters.
Early Life & Student Accomodation
The Stepford Cuckoos are revealed to be actual clones of Emma ' Silverfox' Frost harvested on Muir Island as a concept to create the mutant cure known as ' Hope' ( developed by dr.Kavita Rao). Without anyone knowing of this project, dr. Rao believed that someone with a mutation capable of both attack ( telepathy) and defense ( diamond skin transformation) would be the key to end the sudden process of mutation.
By abandoning the project, Professor X took the initiative to welcome the sisters into his mansion as they became students during the late '90's early 2000's as they were students even during the battle at Alcatraz. Dr. Rao developed Project: Leech instead.
It's not clear if the sisters remained at the institute and joined The X Men although with no other options, it would seem most likely.