‘Breach, violation or non-performance’ is just an example of the kind of problem encountered by translators working out of English. I have met native speakers of German who prefer to work into English largely to avoid this problem of contract translation.
What do the doublets or triplets mean? Probably the lawyer who drafted the contract wasn’t sure but used an established phrase.
How can you find out if they are synonyms or not?
Books on using plain language in the law can be helpful, because they sometimes say which doublets are synonyms and which aren’t. For instance, Mellinkoff, Legal Writing: Sense and Nonsense has an appendix B which lists coupled synonyms.
acknowledge and confess act and deed annual and set aside authorize and empower conjecture and surmise covenant and gree
and many more.
The problem is mentioned by Enrique Alcaraz and Brian Hughes in Legal Translation Explained:
There is, of course, the possibility that the original phrase contains a mere tautology exhibiting neither subtlety nor rhetorical aptness, i.e. what is sometimes called ‘a distinction without a difference’. If this is the translator’s conclusion, there would seem to be two options open: silent simplification by dropping the less general term, or simple reproduction. Lawyers, after all, are not always breathtakingly compelling speakers or writers, and it is likely that most languages would tolerate literal renderings of rather weak pairings like ‘final and conclusive’, even if conscious stylists would not applaud them. On the other hand, the doublet ‘alter and change’ is a candidate for simplification to the equivalent of ‘alter’ or, alternatively, to some such treatment as ‘alter in any way’.
The problem is also addressed in this paper:
Exploring near-synonymous terms in legal language. A corpus-based, phraseological perspective Stanislaw Gozdz-Roszkowski ...Zum vollständigen Artikel