This is the 10297th most frequent Turkish word.
beyanlarıdır
It means "are his/her/its statements" or "are their declarations."
In this sentence, 'beyanlarıdır' means 'are their statements,' forming the predicate that explains 'onların' (their) input.
Onların bu konu hakkında verdikleri beyanlarıdır.
It's their statements on this subject.
Here, 'beyanlarıdır' signifies that what is being referred to, the 'belge' (document), represents the 'tarafların resmi' (official of the parties) statements.
Bu belge, tarafların resmi beyanlarıdır.
This document contains the official declarations of the parties.
In this usage, 'beyanlarıdır' indicates 'are the declarations,' emphasizing the perspective of the judge concerning the statements.