Even in row house you should have a piece that is exclusively yours. If this is the case, there are rules to respect in terms of putting plants or objects on the limit between two properties.
Normally, if an object or a plant/tree is over 2 m high, you need to place it 1m away from the property limit.
I believe it is the only thing that they can get you on. Trampoline is not a building, it is a movable object, so just ignore.

We have the same story with our neighbors over the playground that we installed. They threatened to go to court and all that. I asked our local commune representative to look at it and they said there is no legal basis for complaint. Since then they have left us alone.