Help my ducks are fighting!

I would removed the 2 drakes at once! Look and see which drake is the best for your hens, try putting all the females and 1 drake in a separate place and see how they react, then take the drake out and put a different drake in, the hens would have picked their mates but their can be only one male, If you build separate coops for the two possibly three 1 drake and 2 hens you might be able to stop the fighting, this would mean that the drakes would have no contact with each other,
when you do the test with the all females in with one drake look at which drake your hen's prefer most.

 

This phase will pass if they are left to sort it out. It is called pecking order. All birds do this. There is always a top drake and a duck. At some point you will have to bring your duck ratio up or your drake ratio down, preferably before the aggressive mating season of spring and the more milder fall. Some breeds are more aggressive than others and some drakes are more milder than their buddies. This will take some observing on your part for the proper selection.

 

Drakes need around 4 hens each or hey will fight over them, I would choose the drake you want the most them rehome the others. Drakes can be very aggressive with the ducks and can kill or badly injure them while trying to forcefully mate with them. I hve heard of them drowning them and ripping all the feathers off of the head.