Erich String Orchestra

Eldritch 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.

Chronology
They made their first appearance in the Overlord series under the form of Yuri Alpha and Lupusregina Beta. Alongside 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.