Reinstalling previous employee's MacBook Air's

I have a bunch of MacBooks Airs that needs resetting to be used for new employees and/or developers. Tho they are all locked behind Apple ID's and each employee installed them them self once they got them.

I have been trying all possible button combination in order to enter terminal or to erase the device to a veggie state.

I don't reach the terminal and it does not erase the disk from the Recovery Assistant.

I only return to the This mac is linked to a Apple ID page.

How do i go about to just reinstall them. Without keeping anything on them or any references to a previews employee?

None of the bellow gave me any answer:

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