Shouldn't this be translated with ‘should’, ‘ought’ or ‘will likely’ somehow? It's hard because it's in the future though. I think in English one simply wouldn't translate the future and let ‘on Sunday’ serve as enough indication of that.
According to the english sentence i thought it would be "nós anunciaremos...". Dever = must. Then, the future would be "we will have to announce...".. weird.. but, that may also mean a possibility "we may announce..." anyway, it doesnt match to what duo proposed.