All signs point to no compression in a cylinder... I had the same problem and had to pull heads before determining it was a cracked block... but its possibly a bad valve or bad piston rings... I would guess maybe you'll need to rebuild ur heads at the worst...

 

its time for the compression test it may just be a tight valve or two. the last time I had this problem was on an old truck I had had a dead hole did the compression tests and the compression was about half the other cylenders no difference between wet and dry. I removed the head to find a burnt valve. new valve some lapping compound and head and intake gaskets it was right a rain total cost was less than $100 much less than a rebuild I think bad valves is a worst case scinario