When using 2 engines together with a common power output is there a
simple way  to assure that both engines are contributing equal power?
I can imagine that one or the other could be doing more work even
though they both are running at the same rpm (obviously). I'm thinking
of using 2 of the smaller available rotary engines on the helicopter,
but my question could apply more broadly to any engine type.

John McEverett

You could measure the torque on both engines.
Blue Tooth strain gauges on the output shafts.

Paul Lamar