That will never work! You must deliver two at a time.

Divide angels into a and demons into B.

aaaabbb

AB, get on the boat. One, come back.

AABB B

BB get on the boat and b come back.

AAAB BB

AA ABoard, ab back.

AABB company

AA, come back on the boat.

BBB AAA

BB get on the boat and b come back.

BB get on board

All right! it's over