(found this on Steam, it's pretty easy to get all the endings tbh)
End I : Side with Randal at the announcement. Requires a high Mavvar rep.
End I (leader variant): Have a high rep with all factions and choose "my rebellion" during the announcement.
End II: Side with Andrei at the announcement. Requires a high Golgotha rep.
End III: Side with Saorise at the announcement. Requires a high Iscari rep.
End IV (Special End): Complete End III as well as both Heath's and Randal's Special Ends to unlock it, then play through again as a Golgotha. Select the choices highlighted in red.