Is it possible for the same soul to be within two bodies simultaneously?[1]
When a soul is found inside of a body it is limited to that body and cannot enter another body simultaneously, as a soul can only be found in one body at a time. The reason for this is because when a soul enlivens a body its essence is found in that life-force that is revealed in the body and is hence grasped by it. It is for this reason that the Zohar states that one time the Rashbi asked Eliyahu Hanavi why he was not present in the Idra and Eliyahu replied that he was busy saving the life of Rav Hamnuna Saba and his colleagues. Eliyahu had to invest himself in a body for this purpose and since he was in a body it was grasped by the body and could not be anywhere else at that time.

Can a soul that is not in a body be found in two places at once?[2]
When a soul is not in a body, its essence is not grasped or limited by any specific area or level and therefore, it is possible for the soul to have representation of its spark or ray in many different areas. Thus, we find that Eliyahu Hanavi visits every Bris Mila, even though at times there is more than one Bris occurring simultaneously, and in different parts of the world, as it is only a spark and ray of his soul that attends the Bris, and not his soul’s essence or his body.

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[1] Sefer Hamamarim 5666 [Hemshech Samech Vav] in name of Kol Berama on Zohar

[2] Sefer Hamamarim 5666 [Hemshech Samech Vav] in name of Kol Berama on Zohar