They were on two separate (but bonded) pontoons AFAIK.
Experts (probably from other companies) here said they should have used cranes with "tank tracks" instead because these are more stable on pontoons.
One issue with the first crane was that these kind of mobile cranes (with truck wheels) have a safety feature that will render the crane completely uncontrollable as soon as the bottom of the crane is not exactly horizontal (say 1 degree or so). So even IF the driver tried to correct the situation, he simply couldn't because of this.
I sometimes work with certain platform lifts and they have "angle detection" too, and some things will work slower and some not at all when they detect a certain level of banking....
I also heard the city went for the company that offered the cheapest price (of three)
What I wonder is why they simply didn't use floating cranes like these: