Two drakes and two hens
Okay
So currently your chickens are in a lot of danger, if a drake mates with them, he could kill them. Its very dangerous to have drakes with chickens.
Getting two ducks won't help much, it will actually put those two females in danger. The correct ratio is 3-6 hens per drake. A ratio of 1:1 can result in severe over mating which makes injury likely. Drakes can kill female ducks if they gang up on them or accidentally drown them. It's really important to have a good ratio during mating seasons.
Here's what I would do, separate the drakes from the chickens. Don't get any hens unless you can keep the proper ratio. The drakes will be fine together, a little aggression this time of year isn't unusual, their hormones will be going a little crazy. You can limit this aggression by giving them a kiddie pool each, rather than having them share, and multiple feed/water stations may also help.
Whatever you do, please do not keep these drakes with their chickens, and please don't give them only a couple girls, they would be in serious danger, especially this time of year. You'd probably need a minimum of 6 female ducks to keep them happy and healthy.