Fred is correct. But baring knowledge of German and Russian; hiring a bilingual guide might be much less expensive than renting 35 audio devices & might possibly be more informative. I know a handful of guides I can check if there is any interest.
Fred, you seem to like languages so I thought you might be interested in this from Wikipedia.
Hungarian 9,896,333 (99.6%) The only official language of Hungary. Of whom 9,827,875 people (98.9%) speak it as a first language, while 68,458 people (0.7%) speak it as a second language.
English 1,589,180 (16.0%) Foreign language
German 1,111,997 (11.2%) Foreign language and co-official minority language
Russian 158,497 (1.6%) Foreign language
Romanian 128,852 (1.3%) Foreign language and co-official minority language
French 117,121 (1.2%) Foreign language
Italian 80,837 (0.8%) Foreign language
Interestingly enough Romani is not listed. But with a little research I found a number of Romani speakers in Hungary to be about 260,000 or about 2.6% of the population. Hebrew possibly 0.1%
Of course this has absolutely nothing to do with topic at hand. The WWII document will be in German and Hungarian and the Cold War documents will be in Russian and Hungarian. I have Hungarian friends who lived through the Soviet occupation and they were forced to learn Russian. So anyone over the age of 40 more or less will have some knowledge of Russian; which, yes, is not supported above.
Really, really old folks from high class families would very possibly have been raised in German because that was the language of the elite until the mid-nineteenth century as a rule and into the early twentieth century to a lesser degree as Hungarian Nationalism began to shape society.