If both of these cards are on the field, how are their effects resolved?
No Monsters can be Special Summoned. Both Monsters have a Continuous Effect (page 14 of PDF) that is active while they are on the field. BSotAbyss blocks all non-DARK Monsters from being special summoned, so when you Attempt to Special Summon a DARK Monster, it is BSotHeaven that blocks you, and vice versa when you Special Summon a LIGHT Monster, it is BSotAbyss that blocks you.
The Barrier Statues prevent any Special Summoning, unless the Monster is of a matching Atribute (page 11).