My pair was sharing a tank (30 long) with another non-breeding pair. They were excellent parents up to a point, which seemed to last longer with each successive spawn. The first time they did hatch the eggs, but the wigglers disappeared before they were free-swimmining. By the 5th (and final) time around the other pair had been moved out, and the fry were free-swimming for a couple weeks before they started disappearing. Apparently it wasn't just the other pair that were picking off the fry.
I did find 3 fry each from the 2 previous spawns that had managed to survive on their own, and I have between 1-2 dozen from the last spawn growing out now. I moved the parents to a 55 to take a break from spawning, and to allow several broods of BN fry as well as the little cichlids to grow out.
Do your pair hang the wigglers among plants, or keep them in pits dug in the substrate? Mine haven't stopped showing their spawning colors since they started, even after being moved to another tank. I really like them, mild-tempered fish overall, and great colors/patterns.