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Remember this Gojo jutsu Tobirama used. Hiruzen knew about this jutsu and Tobirama also said this is first time he used it on himself which means he used it before with his own Edo summons. So he was most likely using it against Uchiha´s. This jutsu has great AOE so it probably wrecked plenty of Uchiha´s.
Now do you guys think Tobirama used fallen Uchiha´s as his summons. This would have huge emotional impact on Uchiha´s. Imagine seeing your fallen comrade resurrected. How would they feel knowing they must fight their own brother,father , relative or friend.