This is serious matter. We have to make clear some facts:
SH, locations and influences:
Zoro: He's in the fallen shikearu kingdom, in kuragana Island / Grand Line / Along with Perona and a mysterious man…
- Well, Zoro wouldn't be able to return by himself to SA. We don't know if he's near to the archipielago. He's formed a bond with perona (weak, i think), and yet we saw a mysterious man near some ruins.
CONCLUSION: Zoro's pretty fucked up here, except for the fact that Perona may now how to navigate, or that mysterious guy knows something that would take him to Rayleigh. We have to note, though, that he's nearer than some SH, to SA, he's at least in the Grand Line.
Usopp: He's in Greenstone, an island of the Boing Archipielago / Grand Line / Along with Heracles.
CONCLUSION: He has good possibilities in returning sooner. At least he's with someone who MAY have a boat or something, but there's one problem here: Usopp now is as fat as a sumo wrestler... That fucks him up...
Sanji: He's in the kamabakka kingdom, in Momoiro island / Grand Line / along with Okamas.
CONCLUSION: Sanji has very good possibilities of returning sooner, cause of the (probably) connection of the okamas in the kingdom with the revolutionaries (the whole Ivankov thing). Also, it's probably that they have boats there and sanji knows how to navigate ( he had a boat, remember?)
Nami: She's in Weatheria / In the Sky / alongside Haredas.
EDITED CONCLUSION: Based on the coverstories, there's apparently an easy way to get out of the sky island ( and get back too) However, we don't know the sea that's down weatheria, and that's surely something of concern. Nami is the navigator, and she will have good possibilities to return to SA herself, maybe weatheria has some kind of vehicle faster than a normal boat ( like a type of waver?).
Chopper: He's in the Torino Kingdom / South Blue / alongside giant birds and "wanting-to-eat-him" inhabitants.
CONCLUSION: He's pretty fucked up. He's in the south blue ( not even the grand line ), he's with unreasonable people and mounstrous gigantic birds. However, there's the slim chance that he could actually talk to the birds and tell them to take him to SA (maybe he'll ally with them and defeat those people in order to win their trust), and the he'll be in a better position than other crewmembers. In case that fails, then he'll have to make/find a boat, go to the Redline, and go all the way to SA, and that's seriously a no-no.
Robin: Tequila Wolf / East Blue / Revolutionaries + (non canon? Soran)
CONCLUSION: She probably has the best chances of returning sooner to SA. Although she's not in the Grand Line, The revolutionaries will clearly help her ( cause she is valuable to them: for her abilities (poneglyph) and for being a nakama of luffy, Dragon's son ( in a lesser extent though, maybe because that's not knowed among the revolutionaries (the fact of Luffy and Dragon's relation). Her Knowledge is a plus here too, and she may know how to navigate ( in case the first fails).
Franky: He's in the Future country Barujimoa, Karakuri Island / Grand Line / Kitton Taroimo and The cyborg dog.
CONCLUSION: He's in a good position. He's in the grandline and he actually finded Vegapunk's abandoned house. It's a futurist Kingdom so they should have some transportation vehicles, more powerfull than simple shps or boats. He'll actually find somethings to upgrade himself too ( don't know if that refined version is canonical), and he actually had good navigation skills (he builds ships..)
Brook: He's in harahettania, Nakamura island / Grand Line / Sattan summoners + Longarm Tribe inhabitants.
CONCLUSION: He's in a good position. He's clearly better than other SH situations, People believe he is the demon so they will give him everything he wants ( maybe boats and such) but that will not come free, he would have to defeat the longarm tribe ( and now he's writing a song, that should help) And we know he has at least average navigation skills ( he navigated alone in TB and also was the captain of the rumbar pirates for a while. Don't tell me " But Luffy is a captain but he doesn't know how to navigate" because Luffy is an special case , he's an idiot).
We can say some SH are in better positions than others.. Some are not even in the Grandline, but they will eventually show up, i think One by one in SA ( if Oda doesn't make a timeskip)
Luffy will not be able to go and find them, he's stupid, and he actually doesn't know where they are, and also that would be very boring(returning to where laboon is and waiting for them there isn't an option)
Maybe non canonical As of the anime, they all showed their Rayleigh VivreCard so they know where do they have to go, and they'll probably not wait for luffy to go and get them.
That's it, Long post, phew...