Highly debated topic, its almost entirely dependant on whether or not u beleive that the Sharingan (tsukuyomi) can effect Pein/Nagato - People can speculate either way primarily due to the J-man fight with Pein and the use of his sound genjutsu - some people claim that Pein fell under the genjustsu while others speculate that it was a trap for J-man so he would let his guard down.
You then also have to take into account whether or not a genjutsu effecting one Pein effects them all due to their joint senses or whether it would only effect one.
In regards to ability - Sasuke and Itachi both have the skills and tactics to defeat Pein as they are for more experienced than Naruto with tactics BUT then you also have to think about the intel that Naruto received BEFORE he ever fought Pein - and that he could prepare for the fight with Sennin Mode Clones.
Would Sasuke and Itachi be able to figure out the secret of the Rennigan and prepare or would they just end up fighting the Pein's endlessly.
Also, would Amaretsu be pushed away by Almighty Push?
Guess we wouldnt find out unless it actually happened, what do you think?
Also, this should be in Vs thread =D