Get the wiring right, and if everything stays in sync it could work, but might just result in a release of magic smoke. I suspect this is the most likely outcome (just my opinion as a result of gut feeling). PWM controls work by switching on and off. If the two parts are totally in step into a common load, fine. If not, both are trying to power the full load as individuals, plus, they are trying to feed power into the other power output. This rarely ends well. Since I have no idea what is inside the sealed box, thats just guesswork.
A fairly useful gauge/current chart here -
https://jascoautomotive.com/automoti...apacity-chart/
While it stops at 30A for 16AWG, you will note that the shorter the run, the more current will be carryable. What it doesn't mention is that silicon based insulation can survive higher temperatures than lesser materials, thus the same gauge can carry higher current.
In the distant past, when ESCs were exotic and expensive, I created my own using servo electronics, replacing the tiny motor with a pair of optical isolators that drove higher voltage and much higher current transistors to get a much higher power EC than was otherwise available. The only limit to the power available then was the transistors available. This is still true, but transistors have improved greatly - there are probably some that would work for you, but instead of butchering a servo, there are very cheap 10A (and no, I don't trust that number, either) ESCs that could drive such an output stage in a much more civilised manner.