What colour are they eggs?
If they're white they wont hatch.
If the discus is huge, it might pose a threat, if its still small the kribs will keep it at bay. Same goes for the BN.
The rest shouldn't really be a problem.
Ram vs Krib would be pretty even in size, so not sure how that will play out.
Disappearing eggs could be due to all sorts of things.
Parents eating them, others eating them.. hatching? etc etc