Getting two engines to power 1 transaxle at the same time if they’re both using the same fuel for one, unless it’s a RE/RD with 1 engine powering each wheel. Then the issue becomes timing. Even a millisecond difference in timing will cause the wheels to become unbalance and accelerate at slightly different speeds causing a fishtail effect.
One a two engine, two fuel setup, the issue would be switching the drive train from engine to engine which is bolted directly to the crankshaft which to my knowledge is an internal part of the engine. Somebody with better car knowledge would need to chime on on the logistics of that one.