While I have never done it, it would seem to me that with a 50 and a 100 amp breaker, both would trip around 110 amps. With parallel circuits of equal wire gauge size, the current would flow equally over each conductor (path of least resistance). When the 50 amp breaker saw 55 amps +/-, it would trip sheading its load to the 100 amp breaker which would now trip with a 110 amp load.
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters