Amida triad (阿弥陀三尊)
Amida triad is one style to place a Buddhist image in Buddhism.
It is a triad style and consists of Amida-Nyorai, i.e., Amitabha Buddha at the center and two attendants, Kannon-Bosatsu, i.e., Avalokitesvara Bodhisattva on the left and Seishi-Bosatsu, i.e., Mahasthamaprapta Bodhisattva on the right.
(The "left"or "right" in this case is the direction seen from Amida-Nyorai.)
Kannon-Bosatsu is said to be the embodiment of the Amida's mercy and Seishi-Bosatsu is that of the Amida's wisdom. The Kannon's crown displays kebustu, a small image of Amida, while the Seishi has suihei, a small water bottle, so you can tell one from the other with ease relatively.
In Japan, ancient examples are: The Amida triad made of bronze owned by the Tokyo National Museum, once dedicated to the Horyuji Temple as one of 48 Buddhist images (important cultural property), and the Amida triad also made of bronze enshrined in the Lady Tachibana's Shrine of Horyuji Temple (national treasure).
There are various forms of triads: Amida is seated in the center with statues on both sides standing (e.g. the triad in the Ninnaji Temple in Kyoto), all three statues are standing with Amida in the center (e.g. the triad in the Jodoji Temple in Hyogo), all three statues are seated with Amida in the center(e.g. the triad in the Seiryoji Temple in Kyoto), or Amida seated in the center and the other two statues are kneeling down (e.g. the triad in the Sanzenin Temple in Kyoto). The triad with Amida seated at the center and the other two kneeling down on both sides is a form of Raigo, which means inviting the dead spirits to heaven. The left Bodhisattvas Kannon in this triad usually has a rendai, a lotus-flower-shaped pedestal to carry the dead.
There exists another formation made of 5 statues that includes Jizo-Bosatsu, i.e., Ksitigarbha Bodhisattva, and Ryujyu-Bosatsu, i.e., Naagaarjuna Bodhisattva.
Major works in Japan
The triad in Konjikido of the Tyusonji Temple in Iwate (Three-statue composition, the center one and the two on both sides, made during the Heian period and now are national treasures.)
The triad in the Seiryoji Temple in Kyoto (national treasures, made during the Heian period)
The triad in the Ninnaji Temple in Kyoto (national treasures, made during the Heian period)
The triad in the Sanzenin Temple in Kyoto (national treasures, made during the Heian period)
The triad in the Jodoji Temple in Ono city, Hyogo (national treasures, made by KAIKEI during the Kamakura period, placed in Jododo)
The triad in the Horyuji Temple in Nara (national treasures, said to be the Buddhist image the Lady Tachibana had, made during the Nara period)
Reference: Amida triad in a Zenkouji style