Wait for the fecals....you are doing everything right. If the fecals are clean, they are probably having a growth spurt and in a lanky stage. Personally, I'd get the baking soda out of there and refresh the minerals. The salt in the bs will prevent them from eating enough minerals, and in humid weather, minerals get yucky fast to fussy goats. I keep a box of bs nearby and we all check on our goats at least twice a day, usually more often as they are so irresistible. Stinkin' cute.
Make sure the condition chart you are using is appropriate for your breed. The first time I saw a condition chart I used it, not realizing it was for Boers and I have dairy mixes. The correct condition for my 24% Boer is going to be very different from my Alpine/La Mancha.
If they were here.... No free choice baking soda, that is why they are not eating the loose minerals. Check the noble goat to be sure it has AC in it (not all Noble goat does). And I would up the noble goat ration provided it has AC in it. Read "Feeding Adult Goats The Roughage and The Regulator" on my blog, I think you might find it useful.
a boer goat with dairy in it can stay considerably thinner than a full-boer.
Our whethers are getting 3% grain a day of their body weight, or more.
If They are young growing animals, especially with some dairy in them, they will get thin looking at times if you aren't pumping the grain or alfalfa to them.
Worming is my first action, with goats that aren't keeping enough finish.
You of course now, there is the cocci, the blood sucking worms and then tapeworms. Tapeworms will keep a kid slow growing, but not kill the kid or even show signs of anemia. Tapeworms don't always show up on the ground in their poop, they have to have a really high load to start to see tapeworm segments when they poop.
Did I miss how old these boys are?
the only way I know you are going to see weight improvement, other than fixing a worm problem is upping the grain.
To give you some idea our 4 month kids are getting 3 lbs a day, that is 9 cups of feed a day. yes, we are feeding them out for the fair and pushing them hard.
When ours need to put on flesh we offer free choice alfalfa and add in beet pulp in addition to their regular grain ration. It's worked really well for us.