I'll let an expert give you an expert opinion on this.
A 2 queen hive is possible when there are two seperate brood areas, usually to much honey is separating them or a queen excluder or something.
I believe Queen Bees do tolerate one another if one is the mother waiting to swarm, while the other is the daughter waiting to take over the task of egg laying. If they're around one another to long they might out right kill each other, for now though they will get along until one gets the idea to leave.
It wouldn't surprise me at all if 2 queens beehives sometimes occurred naturally. Yellow jackets seem to be doing it in some locations, and it's certainly seen in some species of ants (the invasive fire ant is a shining example of this).