Scale.
The ants are feeding on the honeydew - sugary excretions of the scale.

Uh oh, I'll bet that the 'brown dots ' are the young crawlers emerging from the egg sacs of the scale insects.

Thank you- so the problem is scale? If I google that, I suppose I can find solutions... Do you have any advice?

No question about the ID -- they're scale.

Start with removing all that you can see then obtain and use the appropriate spray.