I have had several pairs breed together in the same tank. A lot of the time I do it intentionally. If I have a pair that has shown signs of spawning but have never done so, I will stick them in with a breeding pair of something else, or visa versa, and a large majority of the time, it has worked very well. I Also had a pair of Jags, Zonatus and Hoga all spawn in the same tank at the same time. That was definitely a site to see.
As for your response dogofwar. It is quite possible that a breeding pair of whatever can have eggs fertilized by a different male in a different pair. Some male species do spray, they dont have to be right on top of the eggs. My male red devil fertilized my female Xilo's eggs through a divider and the eggs were easily a foot + away from that divider. Hundreds of little fry 4 days later. So you dont have to be an incompetent hobbyist to have something like this happen. Stranger things have happened.
As for your response dogofwar. It is quite possible that a breeding pair of whatever can have eggs fertilized by a different male in a different pair. Some male species do spray, they dont have to be right on top of the eggs. My male red devil fertilized my female Xilo's eggs through a divider and the eggs were easily a foot + away from that divider. Hundreds of little fry 4 days later. So you dont have to be an incompetent hobbyist to have something like this happen. Stranger things have happened.