Formant dynamics of Spanish vocalic sequences in related speakers: A forensic-voice-comparison investigation

•Pronunciation vacillations exist in Spanish vocalic sequences: diphthongs/hiatuses.•Curve fitting is used to parameterize F2-F3 trajectories of 19 vocalic sequences.•Overall forensic performance is very good in a classic scenario (Cllr = 0.15).•Adding related speakers deteriorate system performance: mostly because of MZ twins.•More investigations with similar-sounding speakers (non-twin brothers) are needed.