Erich String Orchestra

Erich String Orchestra (エーリッヒ擦弦楽団) is a group of musicians that serve under Chacmool in the Great Tomb of Nazarick.

Background
Presumably, these Greater Doppelgängers were created either directly or indirectly by the guild member, Temperance.

The Paladin of the Holy Kingdom Arc
They made their first appearance under the form of Yuri Alpha and Lupusregina Beta. Alongside the summoned Evil Lord Wrath and Aureole Omega, the five Greater Doppelgängers in the form of every Pleiades member except Narberal Gamma were present when fighting against the Sorcerer King, Ainz Ooal Gown.

Strength
So far, the musicians are estimated to be at least over five members strong. They also appear to be Greater Doppelgängers.

Trivia

 * The Orchestra was programmed to refer Temperance as Kurayami no Shirabe.