oh, thoughts this wasn't individual, because that'd be dumb as hell :|
1) Jiraiya wins. Without sage mode it's high diff. With sage mode it's low-mid
2) Mei mid diff
3) theoretically oro should win (oro > Other sanin), but without ET, and off his current feats, mei wins. Oro only has Taijutsu and CQC feats in the manga so far (bar some genjutsu and 1 low level wind tech), that's not enough to take out mei. Mei High diff only because of manda.
EDIT: I just remembered oro has kusanagi. oro would actually take 3 mid-high because of kusanagi.