Another option that might make it a little more practical is to have both personalities have the same class, but different or opposite themes/archetypes. For example, side A could be a Cleric of Pelor and side B a Cleric of Nerull. Both sides will have their own thematic choices that differ from eachother, but could ultimately fill the same role. Combine that with jqavins' suggestion and it might make it work a little better