Obtaining Polish Citizenship from Poland-born Father

My dad left Poland in 1968 and he went to Poland several years ago to get his dual citizenship back. He said he only paid 25 zloty. I'm looking for advice on how to go about applying for my dual citizenship. He has a Polish passport now, so I assume I can apply with his citizen number and my birth certificate, though I have copies of his Polish military ID, birth certificate, and Polish marriage certificate to his first wife (not my mom).

It's hard to find reliable information because there are many companies advertising their services. They seem shady to me because they ask for birth dates right away without quoting their fee.

Does anyone have experience obtaining their dual citizenship from a similar situation from the US?
I have 4 other siblings (same father) and 5 nieces/nephews (his grandchildren) that are interested in getting their dual citizenships too. Is it worth applying together since we all would be applying through my dad's nationality?

I'm located in Chicago. Are there any resources here that are worth looking into?
I work remote and hoping to go to Europe for a longterm trip, so I'm open to applying in Poland, in person, if that would help make things go more smoothly. I don't care about cost, I'm more concerned with convenience and I want to ensure that if I go to Poland, I have all the documents I need. (I'd rather put my money towards travel vs paying more to do all the paperwork in the US.)

I don't speak Polish and I understand there's a requirement to have documents translated by a certified translator. Would I need to do this if I just need to show my birth certificate? (My dad has the Polish spelling of our last name. I was given the original spelling of our last name at birth, so my birth certificate has both my parents last names as the Polish spelling, same as his Polish passport). If I go in person, would I have to bring my original birth certificate?

(I speak Russian and I understand basic Polish words and I can read basic Polish. So I feel comfortable going in person without a translator if that matters.)

I'm also having trouble locating the application! I remember finding it years ago, but I can't find it now.

Thank you in advance for reading this! Any advice would be so helpful!

@winogrona, I have no idea, but I've found this:

polishcitizenship.pl/law/

"The new act provides that the foreigners who in the past had Polish citizenship, but lost them before 1 January 1999, can apply for the restoration of Polish citizenship. It is vital that the acquisition of Polish citizenship shall happen on the day in which the decision on restoring Polish citizenship has become final. This means that the applicant's children shall also acquire citizenship, but only when they were minor on the day of its granting."

Maybe you should contact the Polish consulate in Chicago about this?

@winogrona Hi :) It may be a little late for the reply, but:
1. it is necessary to have your birth certificate to be translated to Polish language;
2. it is also important whether you were born after your parents marriage. If yes, then their marriage certificate will have to be translated to Polish language as well;

3. the application for Polish citizenship confirmation can be found here: file:///C:/Users/malgo/Downloads/wzor_wniosku_o_potwierdzenie_posiadania_lub_utraty_obywatelstwa_polskiego.pdf (pages 2-13)

4. it is not necessary to submit an application personally. In fact, it it easier to submit it by post. Then a certified copy / notary copy of your birth certificate will be necessary

5. also, remember that if you want to apply for the Polish passport, the Polish citizenship confirmation is not enough. It will also be necessary to register your birth certificate in Poland.

I hope it helps!