I don't recall any cursing in half-life, if there is, it is surely cursory.
Hey, I almost made a funny there!^
Anyway.. yeah, half-life is violent, cutting zombies in half with saw-blade guns and whatnot, but the violence is directed against monsters. Of course, they're rather violent against humans, being zombies and aliens, and robots and all. So, it's a tough call there, technically. My judgement however, is that the richness of the narrative elevates the game to the point that violence is not baseless. I consider it like watching a violent war movie, of course it's harsh, but that's the nature of struggle. In the end, the game is about camaraderie, the struggle against all odds for freedom, and how science is a double-edged sword. It's a war game, and a good one.
I'm the father of two young boys, and I let them watch me play the game. I involve them in the story line, and they care about the characters. We discuss the actions and consequences throughout. It's a very thrilling game, so I limit the play to short doses, but then my kids are younger than you, and I'd assume more excitable.
Half-life 2 is one of the best games ever made, in my opinion. I obviously can't speak for your parents' values, but I'd suggest finding a few of the better reviews of the game and let them judge themselves. Maybe even get your dad to play the game with you, it really is that good, and discussion-provoking.
If they balk on it for the violence, I strongly suggest getting Portal: Still Alive, the downloadable XBLA stand-alone version. Itself one of the best puzzle games ever created.
I can't speak for TF2 because I've never played it.