The similarity in twins’ voices has been always an intriguing issue in forensic speech matching, but has become a serious matter of research only recently. The present work is a preliminary study of exploratory character describing the similarities of monozygotic and dizygotic phonation under the point of view of vocal fold biomechanics, in contrast to other siblings’ speech and unrelated speakers. Estimates of biomechanical parameters obtained from vowel fillers are used to produce bilateral matches between MZ and DZ twins and siblings, and unrelated speakers. These results show interesting relationships regarding genetic load and ambient factors in the adoption of phonation styles.