As I said before the solution is really simple. Get some copper nails and hammer them into the bark of the trees. Within four months they will not be producing any more leaves.
Its a bit drastic but better than chemicals
And perhaps in future your neighbour will listen when you have a complaint.
You may just spark off a war so I would be very careful how you proceed.
Even Spanish neighbours can be unreasonable. Mine once complained to the police about the loud music coming off my terrace. Incredible really because at that time I didn’t have a music system set up and couldn’t play music at all. All we were doing was talking (barely above a whisper)
We have since resolved our differences (which came about when she needed a favour from me and not being the vindictive kind I agreed). However for two years she and her hubby would ignore me. I just kept smiling and saying hello never stooped to their level.
But some may go further and all out was can break out – so just be careful – but equally don’t put up with crap whether you are in Spain or UK, it is your life as well.