When it states that it's passed down throughout the main family... yes, it's a given that her father (the head of the main family) knows it. It's not illogical. To even imply that Hiashi is below his daughter in ability is laughable.
No where does it state she learned it on her own. It's not as if she just read how to do it and then did it...she had people teach her how to complete it.
Actually, it's not like Sasuke at all. Sasuke invented Kirin (possibly with Orochimaru's help). He didn't learn it from somewhere else- the jutsu had not existed previously. Hinata learned a jutsu that is passed down through her family and was expected to learn. Sasuke's feat with Kirin> Hinata's feat with Twin Lion Fists.
Yes. Just as it says that nearly every jutsu in NV is difficult to master if one doesn't have good chakra control.
Still not an intelligence feat to be honest.
~Also, I'm not saying Hinata isn't intelligent. She's of average intelligence, possibly above-average. I'm just saying this doesn't make her a genius.

I don't think any female in NV is one. To me, Hinata learning Twin Lion Fists just proves she's dedicated and has good chakra control.