Can Prime Itachi beat Prime Sasuke?

Prime Itachi will beat EMS Sasuke (without Perfect Susanoo), his intelligence will lead him to victory.

Does Sasuke have mangekyou Sharingan while fighting Itachi?

He did not kill Itachi, but the experience was still intense enough to give Sasuke the Mangekyou Sharingan. The eyes are a next level form of the Sharingan only wielded by a few Uchiha. It’s exclusive to the Uchiha clan and one of the three main Dojutsu eye-abilities alongside the Byakugan and the Rinnegan.

Who would win in a fight Sasuke or prime Itachi?

Perfect susanoo wins Sasuke the match, but anything less and i think Itachi takes the prize. Sasuke in Gaiden (without Rinnegan) would beat Prime Itachi. Prime Itachi will beat EMS Sasuke (without Perfect Susanoo), his intelligence will lead him to victory.

Would Sasuke or Itachi have gained an EMS?

So in essence yes both Itachi and sasuke would have gained an EMS. Addition: the mangekyo sharingan itself was a actually very rare and many of the uchiha clan had the normal sharingan but rarely advanced to the next level. Izanagi can be used with just the normal sharingan eyes.

What happened to Itachi and Izuna?

At the very end of his life, Itachi revealed his love for Sasuke and sacrificed himself to let Sasuke live. Now combine the two. Itachi and Izuna both allowed themselves to die for love of their brothers. Izuna immediately gave his eyes to Madara while Itachi set Sasuke up to take his eyes.

Is Sasuke’s Susanoo harpoon arrow stronger than Itachi’s Yasaka magatama?

Sasuke’s Susanoo sword is just as much an instant kill due to the Amaterasu flames the sword can produce, but Itachi has the Yata mirror which gives it better defense. Sasuke’s Susanoo harpoon arrow is faster and stronger than Itachi’s Yasaka Magatama but it may not be able to break through Yata mirror.

https://www.youtube.com/watch?v=c7fCwl-cwKE