LCD for filming
Depends on a few factors.
Firstly, I find APS-C cameras slightly easier to manage for precise focus than the 5D2.
Secondly, accuracy is often down to the lenses in use, if it's L's or USM primes with nice wide long throw focus rings then it'll be easier. If it's budget zooms or AFD / micro-motor primes then it can be tricky as the rings are scratchy and very short throw.
Thirdly, old rules of depth of field come into play, keep your moving cameras wide and there's more depth of field latitude. Static cameras are probably better for tele shots where focusing is more precise.
Will the screens be up to the job?
Yes, so long as you get your dof & subject background seperation right, with large apertures it's usually quite easy to see if something is sharp or not, and with the long throw focus rings fairly smooth to alter focus (top tip, look up those silicon jar openers, they really dampen adjustments)
If you've got three cameras you can afford to earmark one as a wide catch all safety shot. Do the pick ups with the other cameras.
Three further bits of advice:
Calibrate exposure off of a grey card with cameras set to spot meter. F no's will not be the same, but centre of card metered centre spot should be consistent accross EV scale on each camera.
Calibrate Manual WB off same. Record 10s under unfiltered light with a QPcard or grey chart or similar. Makes post shot matching easy.
Clap in vision of all three cameras for pic/sound synch.