This is a cool project, but it is far outside the experiences of 99.9% of the members in this forum, the best we can give you are educated guesses.
I have no idea if the motors will push your camera fast enough to overcome any river/stream currents, but I do know that they will make noise, probably too much for your use. Submerged drives will probably work better, like the thrusters used on scale tugs.
Assuming that each motor draws 25 amps (SWAG) then the 5000 mAh battery will run for a total of about six minutes at full throttle. Depending on how much you need you can add more packs in parallel for the same voltage but more run time.
I think you will get better answers in the RC Scale Boating sub-forum. Good luck with your project!
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