hmm they seem large enough to breed. Mine bred around that size, i'v bred this fish over and over. You could try placing them in a tank on their own,if there not already? Put PLENTY of different sized caves, terractoa plantpots work best for me and feed them on a high enriched protein diet (blood worms or something).
When the female gets a dark red/purplish belly and starts to shape its body in kind of an 'S' shape infront of the male to get attention this is when you know they are breeding.
Hope this helps
Jason.
sure fire way: Take a speaker...put in in a ziplock and seal with silicone...place it in the tank...dim the lights...plug it into your best stereo and throw in some Marvin ***e(why cant I say G.a.y.e???)...you know what song