If you're not using Death Immediately in your turn based battle system's setup, the death animations are performed one by one, so while there are still enemies in battle, they're already all dead. Not sure what your custom function checks for, but from ORK's perspective I'd recommend to check for there not being any alive enemies and only 1 dead enemy being there - that'd make this only run for the last dead combatant's death animation.
Regarding #3, that's most likely because there are no free battle spots for those new combatants available. That'd use the Additional Spot setup to create new spots.