Just be patient. I waited since spring for my BG's to pair up. I finally got one pair of BG's to pair, but no luck pairing up the other BG's and my EBJD's with BG's. Just be patient. If there is only one pair in the tank, try placing another smaller male in the tank so the main male can dominate. Try a 20% water changes once every two weeks if its just the pair alone in a 29 gallon+. Slowly turn the heater up.
Overall, just be patient. It will happen. Remember to feed them good food!