Originally Answered: Does Kakashi have sharingan in both eyes? Yes.. But before he don't. As his childhood friend Obito gave his both eyes before his death to defeat kaguya which let him use Susano.
Kakashi got sharingan in both eyes when Obito's chakra transferred to him. Chakra is an essence that connects the world, so Obito's chakra “gained new life” and reanimated the eye for Kakashi. Obito expressed he'd like his friend to become hokage.
Sasuke is an actual Uchiha so both his eyes have sharingan.
They were Izuna and Madara, the first two Uchiha in existence to awaken the Mangekyo Sharingan. Unlike Itachi and Sasuke, who were never both alive with the MS at the same time, and who were not exactly allies either, Izuna and Madara had a loving relationship and both had the MS when they were alive.
It needed another Mangekyou Sharingan to awaken EMS. Well, Yes you can. The prime example for this is kakashi sensei's left eyed sharingan. After half of obito got crushed under the rock while trying to save kakashi, he donates his left sharingan to kakashi as a present for becoming a jounin.
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