I can't really help you with your question, but I can say that discus are ery jumpy fish. The slightest knock on the tank or sudden movement from other fish, they freak. I have recently just got 2 (given to me) they are in with different fish like angels, tetra and even catfish. So far so good but im only 2 weeks in.
I don't know much about bettas only that the're beautiful fish, I would check their water requirements as they might not like a low PH as for the discus at abou 6 - 6.5.