What are the ants underneath leafs in my garden doing?

So a few days ago I spotted a couple of ants underneath some leafs of a major branch of a tree in my garden. Yesterday I had the impression the amount of leafs being occupied by ants has increased a lot what then made me curious. So I spent quite some time yesterday observing one of the minor branches the ants had been very active on by that time. What I figured so far:

Underneath each leaf the ants are gathering, is an insect that looks sort of similar to a fruit fly (gonna call it fruit fly for simplicity, despite it certainly is something different).
Around that insect are varying amounts of dots, which could be eggs or larvae. The ants seem to collect something from the larvae and also seem to be interacting with the fruitfly.

At some point I spotted on the far end of the minor branch 2 living fruitfly. They seemed to be not capable of flight despite having wings. So I concluded they must just have been hatched. They seemed to try escaping the branch, as they pretty directly were just running up all the branch. Having almost made it from the minor to the major branch, the 2 fruitfly came across an ant, which immediately attacked both of them on contact. I was expecting the ant to carry them away then. While being attacked, both fruit fly tried to hide in the attatchment point of a leaf. The ant was circling around the attatchment point of the first fruitfly I was wondering why it did not carry that fly away, since it could clearly geto to that fly. After roughly a minute the ant turned back to their hide, having fully ignored the second fly, after attacking it once, and also leaving the first fly motionless at the attatchment point it was trying to find cover in.

But what happened a few minutes later is what left me astonished.
A few minutes after the 2 fruitfly had been attacked, roughly at the same time, they started moving again. But different then before (kinda looked as if they had been injured but not killed by the ant). They did not seem like trying to escape the branch anymore. But just slowly moving to the next leaf in range continuing for 1 to 2 centimeters going underneath the leaf and then stopping there. Pretty much being in a position, as a fruitfly is positioned underneath the other leafs, where the ants are gathering .
After like 4 or 5 hours 1 ant for the first time scouted the leaf these 2 flys went on. And in fact, other than attacking them again, this ant interacted with the 2 fruitfly¹ like the ants under the other leaves interact with the fruitfly positioned on those leaves.

By now (over 12 hours later) the 2 fruitfly are still there I just checked and the small fruitfly that was only being attacked once, disappeared. The other one still being at the very same spot it moved to yesterday, tho. I would consider them being dead. But I am not even sure about that.

So what exactly are the ants I observed there doing?

If any other pictures would be helpful ask for it, I can take them later today.
Also I have a speculation what it could be that was going on here, but not sure if that would anyhow improve this OP.
Oh, since I can’t identify the species, it might be useful to know at least: this is happening in Bavaria – Germany

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¹ well with 1 of them, the other that had just been attacked once, was simply being ignored