I didn't read any posts on this thread, I pretty much just wanna state my opinion.
I guess Jiraiya and Naruto would have a pretty easy one as long as they keep some distance to each other so that Itachi couldn't use a genjutuso on both of them at the same time. As far as Amaterasu goes Naruto might be in trouble if Jiraiya gets captured long enought in genjutus, otherwise Jiraiya would just seal it away.
Anyhow if they avoid geting hit by Amaterasu wich seems quite possible to me as both, Naruto and Jiraiya are pretty fast in sennin mode, they won't have any problems I think. I guess both Jiraiya as well as Naruto could break easily through Susanno which also costs a lot of chakra. And we have seen Jiraiya being incredibly fast with that one jutsu he used on the summoning Pain not quite sure how it is called right now. So he could force them with this jutsu to keep Susanno up and Naruto prepares his Rasenshuriken in the background with mabey one clone in the front just to distract the brothers for a second.
Also Itachi stated in my opinion that he could not beat Jiraiya although there have been 3 years in between that statement and the time i assume this fight to happen (if both Itachi and Jiraiya didn't die).
Very last I would like to point out that Sasuke and Itachi don't really have any practise with each other, Naruto and Jiraiya have been training and fighting together for over 3 years so imho their Teamwork would be way better then the Teamwork of the 2 brothers.
Cheers, Sominus