If the translation is 'That's for them' I would expect 'To jest dla nich'. Would adding 'jest' be wrong?
To (jest) dla nich= this/that is for them
it's because of "to". You can omit "jest" or "są" after "to".
(do you remember "kot to zwierzę" sentences form the defining lesson?)
Also we have no way of distinguishing this is and that is = both are "to jest"
Nich is a version of "ich" that is used after preposition. It is Genitive and Locative form of "oni/one", and Accusative form of "one".
the whole thing with hints is very strange. I think they stopped adding cases after a while, so some words have all of them, some are incomplete, like this, and some do not have them at all.