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If Salas is the name of a place, there is no plural but the possessive case can be made for Salas's... e.g. Salas's schools, Salas's aging population.
Hank Salas's birth name is Enrique Salas.
Adolfo Salas's birth name is Adolfo Domnguez Salas.
Marina Salas's birth name is Marina Salas Rodrguez.
Rex Salas's birth name is Rex Alan Salas.