To obtain a birth certificate in Poland, please contact the Urząd Stanu Cywilnego - Office of State Civil (Civil registry) territorial jurisdiction. Therefore, you need to know the place of birth of such persons.
Knowing the date and place of birth, you have to go to the office yourself, via the Internet, telephone or post offices in Poland usually do not get.
Our Polish authorities stopped the progress of the mid-twentieth century, or nearby.
I mean, they have all the necessary equipment, internet etc. but what use, citizen and so come as you will have to. Such thinking is a remnant of the 50 years of communism. A lot of time has passed for the change to the system. Changes are not even see, but very slowly. In larger cities, in some cases, already is not badly, but in small towns ... wish to talk.
It should also be remembered that Poland, since the birth of people with whom you wrote, changed the borders. Finding it may be difficult if the files were in the example. Ukraine, Belarus and Lithuania. In addition, the files could destroy the Germans or the Russians.
Write down where these people were born. Proof, where to look for information.
Yours
Slavko