What I can see in the picture doesn't look to me like anything that would look like a normal dropping. You only need to give calcium to the bird having a problem, not all of them (just making sure there is no misunderstanding). The vinegar may reduce the calcium absorption from their diet, I would not give them that for now. There are many touted benefits of adding it to water, but since you have a possible calcium issue, I would try not to mix the two for now and negate any gains from the calcium supplement. I honestly stopped using vinegar many years ago in the water. My birds didn't like it, and I don't want to put them off drinking, especially in the hot summer months. Fresh, clean water is really all they need.