I'd struggle to justify sending two players away. Letting them scrummage with full packs would be both safe and fair, and I think telling them to each get rid of one player could undermine their confidence in you by coming across as a bit of a jobsworth.
Then in practice there'd be a delay in play while they decide who's going to drop out then get confused when two players from the same team drop out!
Yes it would be confusing.
I can imagine the coach would tell one of the flankers to drop out into the line
and they'd go down to bind 3-3-1 and then you'd tell them, no - you can't have a #8 you have to bind 3-4-0
so the #8 would drop out and beckon the #6 to come back
and the coach would shout - no, no, you idiots, get back - #6 to drop out #8 get back in there
and #8 would say 'but we're not allowed a #8'
and the cach would say 'get back in there'
and you'd say 'look, #8 it's OK, no, you can have whoever you like, but you can't
bind as a #8' ..
and he'd look at you as if you were speaking greek..
and your assessor would be thinking bloody hell what a mess, just get on with it...