I have three cats and two of them are bullying the third away from the food bowl.

Weight loss in the third cat means this has moved beyond a management problem into a health concern, and that changes the urgency. The first thing to do is separate feeding completely and consistently, not in different areas of the same room but in different rooms with doors closed, so that the third cat can eat without any social pressure at all. I know the flat is small but this is the one non-negotiable step because she cannot regulate her intake while the others are anywhere near her.

The dynamic you are describing, two cats who are otherwise calm but resource-guard specifically around food, is very common and usually about the predictability of access rather than about dominance in a broader sense. For the third cat, mealtimes have become stressful regardless of whether the others are physically present, because she has learned that access is uncertain. That anxiety itself can suppress appetite.

Once you have feeding fully separated, the next step is making sure she has enough meals per day in a calm environment to regain her weight before addressing the longer term management. Three meals in a closed room is more effective than free feeding in a shared space. If you want to look at the full picture of how the three cats interact and how the flat is currently organized, the Work With Me assessment is the right tool for building a realistic plan that works in a small space.