"My oldest sister loves his youngest brother."
Translation:Moje nejstarší sestra jeho nejmladšího bratra miluje.
Maybe, but it is not the sentence that was chosen for this course. The sentences must be chosen with a specific learning target, not randomly.
Besides, they are really equally good, please read https://cs.wikipedia.org/wiki/Aktu%C3%A1ln%C3%AD_v%C4%9Btn%C3%A9_%C4%8Dlen%C4%9Bn%C3%AD http://www.cesky-jazyk.cz/slovnicek-pojmu/aktualni-vetne-cleneni/ and https://www.czechency.org/slovnik/AKTU%C3%81LN%C3%8D%20%C4%8CLEN%C4%9AN%C3%8D%20V%C4%9ATN%C3%89 before future comments like this.