Both same - and opposite - sex sibling pairs reported rule breaking behavior, particularly... when both siblings were at a friends house. (content.iospress.com)
The resemblance between these adopted biologically related (N = 106) and unrelated sibling pairs (N = 230) was compared and examined over time. (cambridge.org)
In a sample of affected sibling pairs, both maternal history of mood disorder and current ADHD was a predictor of impairment in family functioning [29]. (link.springer.com)