Tough situation.
If her friends don't like you, that spells trouble. Her being your friend's sister could also spell trouble, but may not necessarily. Basically, in my opinion things are stacked against you.
This doesn't mean you can't give it a shot. Hell, there's probably not much of a problem in bringing it up with her, assuming she's not the randomly vindictive type. If you actually want to go for the relationship, as I said, there's factors against you. As long as things are respectful, I don't think it should be much of an issue with your friend (although, I admit, if one of my friends went out with my little sister, I may be a little weirded out). As for her friends...well, if they fight against you it could put a serious strain on the relationship. "Could".
People listen to their friends, at least on some level, so that could be a problem if they really do hate you. That said, it's not simple failure-inducing factor, and I'd hope they'd be easier on someone a friend's involved with if it wasn't destructive.
So yeah, you can at least find out if the feeling's mutual, but I'd suggest (and this is hypothetical speculation only) giving it a bit of time before actively pursuing anything; see if circumstances become a bit more accommodating.
