I seriously hope you didn't get scammed on these two fish. RFI does not have the best reputation for selling healthy discus or sending correct strains. And this is from both searching forums and personal experience.
As to your question you do not have enough tank space to breed discus unless you are going to cull batches down to almost nothing.
And as for size being a predetermination for breeding that is not an accurate way to judge. Breeding is not determined by size it is determined by age. I have seen 3" runts lay eggs. When you buy a breeding pair ask for age, pictures/video of the pair with eggs and or wrigglers, and when the last spawn was.
Sorry to say you most likely got sold two fish that were showing breeding signs.