...move...
or:
lay your speakers so they aim upstairs, and when they just finished fucking troll them with something... for example play random videos from gaytube.com or chainsaw sound or looped 'applause' sound or what comes to your mind.
When my first kid was born we were suffering from the neighbours as well, a woman above us was wearing high heels at home, we always knew where she walks/is.. pretty disturbing.. So we decided to move out of the flat to a house... 6 years passed since, and during this summer we moved to our very own house, and would never ever move back to such a building you mention...
What if you record them fucking, cut a sound sample from the funniest/most loud parts, than leave the building for a few hours while playing the looped sound clips on high volume. Timing could be perfect when they are sleeping/quiet..