Brining multiple chickens I'm attempting to brine multiple, however I am confused as to whether my brine will be sufficient.
When I usually brine a single chicken I measure the weight of the water that I am going to use and then add salt which is equivalent to 5 percent of of that water's weight. 

This time however I need to brine 4 chickens, and I've bought a 10 litre food grade container for this purpose. I'm wondering if I fill this entire container up with water that must mean i'll have to use 500 grams of salt to get a 5% brine solution, that's a lot of salt. What if I used 5 litres of water instead, and 250 grams of salt, this is still a 5% brine solution, will it yield the same results? How long should I brine for optimal results. When I brine a single chicken I usually brine for 5 hours as i've read that any longer and the chicken will become very salty? (Is this true?) And should the weight of the chickens factor into anything?

I'm cooking for a lot of people and I havent brined at this scale before so any help would be appreciated.
If you stay with the same ratio of salt (and any other ingredients) to water that you normally use, you should achieve the same results. As you normally use a 5% solution it shouldn't matter how many chickens or how much water if you stay with the 5% solution.

The only thing that the weight of the chickens will factor into is the amount of brining time needed. A larger bird will take more time than a small one.

Re time, a good rule of thumb for whole chickens is 2 hours per pound, using a 4% solution. You may want to slightly reduce the time per pound using a 5% solution. So, your 5 hours sounds about right. I wouldn't go over that as I would be concerned that it may make the meat mushy. (Haven't ever done that but I've heard that it can happen if over brined.)