Well OP, you're probably never going to reduce enough sound to keep them happy if that's the case.
If you reaaaally don't care about the looks and PITA involved with doing a little soundproofing, you could pin egg cartons (or just get egg flats from a Denny's or something) to the roof, and hang blankets 6" or so out from the walls, to create a ghetto room within a room. But probably more trouble than it's worth.
We actually did this to our jam room when I was in a townhouse in University. We made frequent trips to a nearby breakfast place that held their egg flats for us, covered the entire roof with egg flats, and went to value village (thrift store) and bought a bunch of comforters and thick blankets which we hung.
Place was pretty ballin', but you could still easily hear the drums throughout the house when I was on them. Still, I was respectful and only played during reasonable hours, and we talked to our neighbours and they never complained. The basement did have thick concrete walls though.
Horrible potato pics my roommate took:
These are both before we finished the ceiling and did a little tweaking, but you get the gist of it.