He's in his 50s and he sits in a hot tub with his daughter and her friends, who have the emotional/intellectual maturity of 13-year-olds, talking about losing virginity and playing Truth Or Dare?
Yeah, that's fucking gross.
And yes, absolutely some teenage girls do flirt or try to act grown-up around 'safe' men, but as PPs have said - the appropriate thing to do is shut it down, not encourage it. Most men in their 50s would feel incredibly awkward about a 14-year-old behaving like that around them and wouldn't be engaging with it. He's old enough to be her grandfather.
'Jokes' that reference rape are fucking disgusting in any context, let alone in the company of a young teenager.
The thing is, even if all this was completely innocent which it isn't, it obviously makes you really, really uncomfortable, so why haven't you dumped him? You really don't have to put up with behaviour that makes your skin crawl, you know, even if he says it's all fine. It might be fine for him, but it isn't fine for you, and therefore you should end it with him.
You have a teenage daughter. I'll be brutally honest: if I had a daughter that age, I wouldn't let your partner anywhere near her in a million years.