If I was in real trouble and no way out, and they had the money, then I'd hope they would help. But I wouldn't demand it. My mother would resent my father for ever if he didn't help me out though (they divorced 26 years ago but she still hates him... so wouldn't do anything except give her a new burning grudge against him).
I've only ever asked my father for money for my sister when she's been in trouble - and I've really had to beg. No problem badgering him for her though, one occasion she would have been permanently disabled if left on an NHS waiting list and another she was pretty close to being homeless through no fault of her own.