According the EuWeb:

The house of Sponheim apparently began with two first cousins, the names of whose fathers are unknown.

One was Gf Stephan von Sponheim The other, and probably senior cousin, was Siegfried, Margrave of the Hungarian Mark (1045-48), Count im Pustertal, +1065; m.Richgard von Lavant (+ca 1072) dau.of Gf Engelbert im Inn- und Norital; they had issue:

• Siegfried, Margrave of the Hungarian Mark (1045-48) -EuWeb; his profile on Geni see: Siegfried I von Sponheim, Graf im Pustertal .
• Stephan von Sponheim -EuWeb almost certain same this profile on Geni.

According the German Wikipedia

Grafen von Sponheim (unvollständig)

Stephan I. († ca. 1080), (gesichert ein Vetter von Siegfried I.),

Stephen I († ca 1080) (certainly a cousin of Siegfried I.)