So, they're around 18 months old and you've seen courting. Like many others said, they look like a pair to me as well.
I'd start pounding them with food and mist more than normal. See if that gets them going for you Dave. You can also try moving things around in the viv. A trim, adding plants, more laying sites, etc. Anything to get the male to want to establish a new territory.
Ok, That sounds like a good idea, currently they have 2 coco huts, plus the leaf litter, but they could use more plants. it's a 20 long viv but there's only 6 or 7 plants in it. they are so bold I thought they didn't need that much cover. oops
It's not really about cover. You just want to mess with things and that may get them going. Change things up a bit...
I trimmed my Oyapok viv once, my hands weren't even out of the tank yet and the male was calling and the female stroking. They were an established pair though.