If this were a pond I was managing... I'd start with a chelated copper (cutrine, et Al.), or copper sulfate treatment, for the FA. It's surrounding your target vegetation and will limit the effectiveness of the diquat. Once the FA is no longer a problem (2 weeks), yes proceed with the diquat. It looks like your a stone's throw from a larger body of water.... Is that salt water? In my experience, ponds so close to salt water can be tough. The salinity tends to "cancel out" or bind up chemical and limit their effectiveness. Your ponds are also small enough that you could rake them pretty quick. Then you would only need maintenance level of chemicals, as opposed to corrective levels. If your cost sensitive, go the rake route.
As for application, no don't just dump. The fountains won't work the way you're thinking for diquat. Mix the chemical in a backpack sprayer and swath it on top of the target. You could mix both diquat and cutrine in a single treatment, but you'd get better results with cutrine, wait two weeks, then diquat.
Picture also looks like the ponds close to a road... Might be a good candidate for dye/aesthetics, and the dye will shade the water to help inhibit regrowth.
Another option, since you're located in Florida, just get a lake management company on the job. I can give you a recommendation, even if it's not me (full disclosure, I run an aquatics company in NE Florida - Jax).
