Siblings share, on average, 50% of their DNA. Each inherits half their DNA from each parent, but which half they receive is random.
What varies is the mixture within each parental line: if your parents have diverse origins, each sibling may inherit more segments from some populations than others. For example, one may inherit more DNA from an Italian paternal grandmother, and another from a Spanish paternal grandfather. The paternal and maternal lines each contribute half. Only identical twins have virtually the same result.