Okay, I'd like to weigh in on this, in our legal system(since we don't really know how the BlazBlue legal system works anyway) it would be entirely legal (and not pedophilia) for any of the other characters to be with Rachel, she is older than them and it is recognized that the age that people are capable of consent is the reason pedophilia is illegal, not appearance. As far as psychologically, that is somewhat of a different story, it really depends on why the other person is attracted to Rachel really, are they attracted to her body or her personality, if it is the former then yes, psychologically it is pedophilia, if it is the latter then I would say no it isn't. That said if it happens to be both then it is pedophilia, as has been mentioned before it is a complicated issue.
Just editting to add a couple of things here,
About the RagnaxNoel pairing, based on what I've seen, I would say that is another hard one, Noel has all of her own memories (although there are a few of Saya's childhood memories rattleing around in there) and thus can't really be considered Psychologically as Ragna's sister, Genetically is a different issue though, it really depends on how close to Saya's DNA (and therefore Ragna's DNA) she is, from how closely she resembles how Saya originally looked I would say that she is pretty close to being an exact clone of the original, so genetically speaking it would probably be considered incest (purely from a genetic standpoint). Interestingly from what I've seen it wouldn't effect the pairing that much as far as the legal workings of the BlazBlue Universe, Tsubaki's family has been in-breeding for generations (as mentioned in Tsubaki's story mode) and there hasn't been any legal reppercussions, in fact they even seem to get married legaly (also briefly mentioned since Tsubaki's parents were mentioned as being husband and wife) so it wouldn't really encounter any legal problems even if it was incest.
That said, I think that Ragna and Noel have much more of a Brother/Sister relationship, they seem to relate much in that way (including their pointless arguing whenever they have a spare moment) and this could be due in part to the fact that Noel looks so much like Saya.
On a more serious note. This man (or woman) should be President/Queen/whatever for being smart and logical.
This post makes the most sense out of anything.
And yea it's totally possible for Ragna to go out with either of them based on this alone.