With middle seats out and rear folded up, definitely can do 20 on the floor knees folded in front. You’ll hit space limits before weight. Crew chief in the back will certainly get cozy though.
In a hot fire situation I can easily see the “no possessions” get to the chopper, but if there’s not a fire issue and only an egress issue I can’t imagine packing in 20 with purses and/or backpack. But I’m in my armchair and not in the situation.
Look at CHP rotor during the Atlas Fire, crammed a bit more in there than available seats, in middle of the night with fire at their ankles…