(First) Elagabalus: The certain tip is the presence of the horn on the forehead. Also, the legend begins with IMP but spells out ANTONINVS.
(Second) Caracalla: The legend does not begin with IMP and does not include 'FEL'. All coins of Elagabalus use IMP except the ANTONINVS PIVS FEL AVG issues.
(Third) Caracalla: The portrait is much too young to be Elagabalus. The abbreviation for Caesar is 'C' rather than 'CAES' which was the only form of Caesar used by Elagabalus.
(Fourth) Elagabalus: The legend starts with IMP and has ANTONINVS spelled out. Caracalla would have abbreviated Antoninus to ANT or ANTON.