"They are the names of Kateřina's brothers."
Translation:To jsou jména bratrů Kateřiny.
I just need to say this out loud because it twisted me up a bit. . . This sentence requires two genitives, because the names are possessed by the brothers and the brothers are possessed by Kateřina, so both the brothers and Kateřina are possessing something in this sentence, and so are genitive.
Edited five minutes later. . . If this is not correct, please say so.
Edited one week later. . . . Passing by this question again, I noticed my post might be considered slightly or unforgivably rude (depending on where you're standing). It was unintentional, but rude nonetheless. Editing for a more polite forum.