There are a lot of variables including age and breed of rooster. Ranges for cock to hen range from 1 to 8 and 1 to 20, these numbers are for successful fertilization. Having to many roosters to hens, can also cause harm to your hens as the roosters will try to make the same number of matings per day regardless of the number of hens, so each hen gets more then her required matting's.
The one hen that is getting matted the most is probably the least dominate, and because the roosters feel the need to each mate about twice as many hens as you have she is getting overly abused.
Obviously there are several methods of changing the cock to hen ratio. You will need to decide which is best for you.
Roosters can be neutered, when altered they are called a capon. This is usually done at an early age and is primarily to increase the animals value as a meat product. There are behavior modifications with this surgery as well. I am not familiar with nor did I find reference to neutering at a mature age.
With 7 hens unless you have a need for a rooster, one is really not needed. From personal experience I have run flocks of 8 to 15 hens through the winter without a rooster. I find that usually one hen will take a more dominate (and noisy) role. If needed an unrelated rooster can easy be obtained in the spring.