have a look under the floor. Where it is not plastered, there may be gaps in the brickwork, and badly mortared joints. Any gaps let noise through. Pack these in with mortar, then lay some dense mineral wool bats (heavier than loft insulation) to fill the space between floorboards and ceiling. Polystyrene is too light. Do the same in the loft, brickwork that is out of sight is often very carelessly built.
If there are old fireplaces/chimneybreasts, the brickwork between your flue and the neighbours may only be 4" thick, and gappy.
If you have room, consider a built in, wall-to wall, floor-to ceiling wardrobe. The hanging clothes will absorb airbourne sound, and the gap and doors will block more. Well-packed bookshelves are also good.
Sound will come through any gaps.
If you are drylining, the heavier the plasterboard the more effective it will be. the frame should be isolated from the wall and fixed at floor and ceiling. Again use dense batts behind the plasterboard.
Try singing, coughing, listening to radio etc so your neighbours are aware of the problem. With luck they will also decide to soundproof their wall
Otherwise, wait until they have been living together for a while, and the passion
will probably die down
