The second photographer is using an 18-55mm kit lens. At 50mm all of Canon’s 18-55mm kit lenses have a maximum aperture of f/5.6.
If one is constrained by using ISO 400 and 50mm in order to match the other camera, then the only variable left is exposure duration, otherwise known colloquially as “shutter speed”.
Since f/5.6 is two stops slower than f/2.8 used by the other photographer, the exposure time must be two stops longer.
Two stops longer than 1/250 is 1/60.
So the second photographer must use 1/60 with ISO 400 and f/5.6 to get the same exposure values as the first photographer using 1/250 with ISO 400 and f/2.8.
This presents another issue, however. Assuming both cameras are shooting video at the same frame rate, the footage at 1/250 will look “choppy” compared to the footage shot at 1/60.