It is a variation of the surname "Sivieri," which is common in the Emilia-Romagna region of Italy. The name could potentially have other origins, but Italian is the most likely based on its commonality and the region where it appears.
To be more sure of the ethnicity, you would need more information, such as:
* Location of family origin: If you know where in the world the family originated, that would help pinpoint the ethnicity.
* Family history: Knowing the family's history and where they have lived over generations can help determine their ethnic background.
Remember that surnames can be adopted or changed over time, so it's not always possible to definitively determine ethnicity based on a last name alone.