When an Empire Sovereign has a Kingdom Faction, and when a Kingdom Sovereign has an Empire Faction, that Sovereign has access to both Life and Death Spellbooks.  Either the Sovereign can only choose a Faction of his/her normal Alignment, or the Sovereign only gets access to normal spellbook *or* the spellbook associated with chosen Faction (Life for Kingdoms, Death for Empires).

Also, I think it would make sense for consistency for the "Kingdom Report" for Empire players be renamed "Empire Report", and "Found Kingdom" ability of starting Empire Sovereigns be renamed to "Found Empire".

Best regards,
Steven.