When it comes to wet brining, it can be a bit confusing at first when the recipe doesn't clearly include up to how much meat in weight you can brine. That recipe can cure up to 48 pounds of meat. So if you can fit all three pieces loosely in the container you can cure them all together. Just don't stuff the pieces in, they should be loose, and every 24 hours move the pieces around and stir up the brine.
There is no maximum amount of brine that you can make for a certain weight of meat, but there is a minimum. For example, you can brine 2 pounds of chicken breast in five gallons of brine mix, but it only needs one pint of the same brine mix to properly brine or cure it. Whether brining in five gallons or one pint; the chicken breast will cure at exactly the same rate. Making too much brine is a waste of supplies, but making too little will effect the quality of the final product. To make sure you have enough liquid for brining; a basic rule of thumb dictates that the amount of brine should come to 50% in relation to the weight of the meat, many sources state 40%. I use the 40% number to insure that I have enough brine, the 40% corresponds to many other recipes; such as what Kutas uses. For his ham recipe he states 5 quarts of brine will cure up to a 25 pound ham. Use either percentage that you feel more comfortable with.
A whole loin weighs 8lbs. - 11lbs. Two quarts of that brine mixture will be enough for 10.4lbs of meat; 3 quarts will be enough to cure 15.6lbs. To save supplies, you can scale the recipe down and make one gallon. That will be enough to cure brine/cure 16lbs. of meat. Though the amount you need will depend on the size of the container, because you will still need to make enough brine so that what ever container(s) you use, the brine will cover the meat. So if one gallon is not enough, you will need to scale the recipe to make enough, or you can go ahead and make the full three gallons and use the amount you need to cover the meat.
Also once the brine is made, say you are using multiple containers; such as you are going to cure each piece into a separate one gallon Ziploc bag. You can distribute that batch of brine between the three bags. Place one piece of loin into a gallon bag, pour in the brine until it is well covered, close the bag - expelling as much air as possible. Repeat for the other two pieces. If using Ziploc bags for curing/brining, always place them on a rimmed baking sheet incase there are any leaks, the brine that leaks out will be contained.