If we see Digica EX03 Set
Dorbickmon line is
Sunarizamon > Flarerizamon > Volcdramon > Dorbickmon
But he also officiallly classified as Digixros so we can assume other Death General also Digixros form
My ideas :
Dorbickmon ( 5 Dragon/Fire Digi ) = Megadramon X Flarerizamon X Brachimon X Gigadramon X DarkRizamon //
Splashmon ( 3 Water / Cyborg Digi ) =
Ranamon X Whamon X Depthmon //
Gravimon ( 3 Earth / Mythical Beast Digi )
Grottomon X Insekimon X Dark Starmon //
Zamielmon ( 3 Wood / Fairy Digi ) :
Arbormon X Ajatarmon X Fairymon //
Olegmon ( 5 Aquatic Beast / Gold/ Metal ) :
Mercuremon X Zudomon X Capt Hookmon X Mermaimon X Blizzarmon //
Neo Vamdemon ( 5 Dark / Demon )
Vamdemon X Devimon X LadyDevimon X Matadrmon X Dracumon