The surname "Prismriver" is sometimes written as "虹川"(nijikawa), which is regarded as the name meaning “prismriver”, although the fact is that it really means “rainbow river”.
It may be coincidental, but Lunasa's name is similar to that of the J-Rock band "Luna Sea".
Lunasa's spellcards, "Guarneri del Gesu," "Stradivarius," and "Pseudo Stradivarius" make references to some of the most famous violin makers of all time, Giuseppe Guarneri and Antonio Stradivari. Oddly enough, the Amati family of luthiers are left out, despite making a fair share of equally good instruments.
Their spellcard background has an image of a score for Last Spring, from Two Elegiac Melodies by Edvard Grieg.
Layla Prismriver, the youngest of the original four sisters, has never had any known official art. Her only mention seems to be in the Prismrivers' official profiles.
Because these three sisters are created Poltergeists who were made by Layla Prismriver to have the appearance and personalities of her three older sisters from whom she had been separated, they are technically all the same age since they were presumably created at the same time. They only act out the roles of oldest, middle, and youngest sister based on whichever one they were made to resemble.
It is known based on their official profiles and from comments by Shikieiki that none of the original four sisters are still alive today, though it is unknown how long ago the events were that spawned these three poltergeists occurred.
Lyrica's name may come from the word lyric, which means a set of words to make a song.