Relationship DNA testing, including grandparent, sibling, and twin testing, is crucial for establishing biological connections in situations where direct parental testing is not possible or specific relationships must be verified. Grandparent testing is often used for legal matters such as inheritance, social security benefits, or immigration cases when a parent is unavailable, while sibling testing helps confirm shared parentage for inheritance disputes, custody battles, or immigration purposes. Twin testing determines whether twins are identical or fraternal, which can impact medical treatments like organ donations and legal matters such as inheritance rights. Overall, relationship DNA testing provides accurate, legally admissible evidence that helps resolve family matters, protects legal rights, and ensures informed decisions based on reliable biological data.