[BXL, WSP]-Neighbour asking us to prune our border/fence trees

I am a one of the two owner of a small apartment building in Brussels-capital region. I also happen to be the syndic for the association of co-propriters.. Commune is woluwe-saint-pierre.

We have about (~20 pine??) trees bordering our garden with the neighbours' garden. The trees have grown tall, perhaps, about 10~15 meters.

The neighbours wrote to us a letter few months ago requesting to cut/prune the tree tops. The problem for them is, they don't get enough light or get too much shade due to our trees.

They aslo claim the previous owners did so few years ago, based on their request. We are still waiting for a gardener who can do this for us at an affordable price.

She is reminding us again with another letter, plus copying to the association of co-propriters for a response/action from us. This time, She mildly threatens that she may take further course of action if needed.

The trees are simply growing tall but not spreading out/branching out.

(1) Are we legally obliged to cut it/prune the tree tops if they offend our neighbours?

(2) What are the legal implications if we are unable to cut these trees soon?

(3) Are there any restrictions in our commune as to how tall the border trees can grow?

(4) What are the implications  if any  of our trees fall to neighbours garden and damage any of their property?