Since childhood I have had a confusion. When our Prophet (ﷺ) made the ascension, he met several Prophets (عليهم السلام). My confusion is when we die, we enter the Barzakh including the Prophets (عليهم السلام).

How come some of them are on different heavens?

Regarding the descendants of Adam (عَلَيْهِ السَّلاَمُ) on the right and left, how come they are on the heavens?

When the Prophet (ﷺ) went up to the heavens on the occasion of the Mi`raj, he met the souls of the prophets, not their physical bodies, as their bodies were in their graves in the Barzakh. This has been mentioned by Shaykh al-Islam Ibn Taymiyyah.

As for why the Prophets were on different levels, then Allah knows best. There’s no reason to ask such questions, and having knowledge of such matters is not beneficial.