This sentence is ambiguous in English, because "were there" can either a verb tense or spatial expression, so you cannot know whether the Turkish should include "orada" or not.
And I wonder how one would say it in the spatial sense?
Orada kaç mühendis idi?
Orada kaç mühendis imiş?
Where is the word there translated?
The "there" can be read with different meanings.
How many engineers were existing? = Kaç tane mühendis vardı?
How many engineers were at that place? = Kaç tane mühendis oradaydı? [maybe?]
Why not muhendisler when it is plural