Inclusion Criteria:  2 or more children in the family (i.e., child with cancer and >1 sibling)  Sibling(s) and child with cancer each under the age of 18 at the time of cancer diagnosis Sibling(s) can be biologically-related, step-siblings, foster-siblings, or adopted-siblings Parent and sibling(s) fluent in English Sibling(s) 12-17 years of age Sibling report of at least mild posttraumatic stress (score >11 on the Child Posttraumatic Stress Scale for DSM-5) Child with cancer must have received cancer diagnosis at least 3 months prior to the family's enrollment in the study  Exclusion Criteria:  A cognitive impairment that would interfere with pilot program and interview completion (as reported by parent) Bereavement Significant externalizing behaviors that would interfere with group participation (as reported by parent)