Itachi and Kisame with high difficult; for the simply reason that Itachi would be in the position to handle two Sannins while Kisame could do it with one.
Sannin, they are just two powerful, oro dying because he made himself vulnerable, jiraiya dying by the hands of a rinnegan user and tsunade still alive leading the fight against madara.
I think it's a shame that sannin are underestimated their deaths seemed lame because of either the opponent they faced or the condition they put themselves in before the fight happened
tsunade alone would be major problems for itachi since she can break open susano and has intel on uchiha abilities. as does oro. oro can say formation of ten thousand snakes and jiraiya will summon two sage toads who are strong in their own right. its essentially 5 on 2 with the two toads. jiraiya changes the battlefield with yomi numa