I couldn't see myself practicing on my sister (kinda impossible since I'm an only child). But if I did have a sister I would ASK her what she thinks of some of my approach tactics. Kinda like a Q&A session with a female. I don't think however I'd "practice" like Kino and what not on my sister, she'd probably flip out and tell my folks, I'd imagine.
Asking would be okay, but think about it, there are TON upon tons of girls you can practice on in the world. Girls you aren't interested in, girls you wouldn't ordinarily hit on, girls you like, girls you love, there are lots of girls out there. Why not "practice" on them? I mean how much different would it be practicing on your sister (who I'm hoping you have NO interest in at all) and hitting on some random girl (who you also haev NO interest in). It just makes more sense to go out into the world, where you can get definate results to study rather then your sibling who's feed back is definately going to be skewed.