various ways in which these surnames can be spelled
Błaszczyk => with l-slash (ł glyph) - pronounced in Polish as English "w", and two digraphs: "sz" (roughly sounding as English "sh") and "cz" (English "ch"). Your American spelling replaces "ł" by regular "l" and skips the character "z" in the digraph "sz". To check the pronunciation of this name you can use one of the two programs:
A. translate.google.com or
B. ivona.com.
When using A select Polish=>English translation, type Błaszczyk in the left field. You should see "Blaszczyk" in the right field. Press the speaker icons in each field and you will hear the difference between Polish and American pronunciations. They sound quite close, because the program A sneakily copies the rules of the Polish sounds into its "right field". Compare it with result of "ivona.com" (program B) and you will hear significant differences.
There is an unpleasant bug in the text-to-speech feature of the program A: it sometimes skips the sound "B" in the Polish (left field) version of "Błaszczyk".
Klepacki => this spelling is correct, the pronunciations in the program A are quite similar to each other, but the program B produces different sounds (American pron. is similar to what you have described in your post)
Siegmund => this is a German version of Latin "Sigismund" or Polish "Zygmunt". He could have been given any of the three versions, depending where he was born and what religion he was born into. Try the sounds of "Zygmunt" using both programs.
Stanisława => with l-slash (ł glyph). Program A incorrectly assumes that it is a male name "Stanisław" and translates it as "Stanislaus". Try it for sounds.
Gostków => with o-acute - pronounced in Polish the same as "u", in English as in "boot". Try the programs A and B for the sounds.
There are two villages of this name in Poland. In addition there is also "Stary Gostków" (Old G.) and "Nowy Gostków" (New G.). See en.wikipedia.org/wiki/Gostków
The surname "Błaszczyk" corresponds quite well with the place name "Gostków". See for example the map of Poland with geographical distribution of the name "Błaszczyk", moikrewni.pl/mapa/kompletny/b%25C5%2582aszczyk.html. The page is in Polish, but the text under the map says:
+ In Poland there are 26 045 people named Błaszczyk.
+ They live in 358 different counties and cities. Most of them, exactly 1749, are registered in £ódź .
+ Other counties / cities with particularly high numbers of people of this surname are Zgierz (832), Warszawa(789), Ostrów Wielkopolski (538), city of Wroclaw (484), Częstochowa (478), Jarocin (382), city of Poznań (368), £ęczyca (333) and Bełchatów (330).