The first one, coming from the right side, could be anything from 12.7 through 14.5 to 23 mm. The rate of fire fits DPshK, NSV, KPV and even Sergey. The second one, from the middle, is tricky. Seems to be a mix of single-shots and slow ROF bursts - so more like a cannon than a machine gun. The third one, from the left, is most likely the 30mm cannon of a BMP/D-2 (2A42), as I've seen it in action and it looked exactly like that.
They are all shooting at roughly the same spot. Unless there's fortified infantry there - unlikely - it's more probable that they are zeroing in the guns, as night optics usually distort the regular zeroing. Definitely not for illumination, as tracers do not provide any. Also, they are using old ammunition, as you can see how often the magnesium-part gets de-attached and flies harmlessly (and uselessly) somewhere else. It happens with all tracer rounds, but the older they get, the more common it becomes.