Polish/Lithuanian/EU citizenship by descent

All 4 of my grandparents were born in Poland so I feel like there should be some way for me to obtain Polish citizenship by descent (or at least some other EU citizenship). My maternal grandfather lost his citizenship when he joined the red army. A few years later he joined the British army (doesn't this count for something?). My maternal grandmother left Poland before the holocaust and she lost all of her documents.

My paternal grandparents were born in Vilnius. They fled the country when the holocaust happened. As jews who were trying to survive, they had to leave Vilnius. I managed to get copies of most of the required documents (e.g. birth certificate, refugee camp documents that state they had to flee the country, etc.). These documents clearly state that they're both Polish. The thing is that my grandfather's dob on these documents is incorrect and it doesn't match up with the dob on his current ID. I think that my grandfather changed his dob during the holocaust because it was necessary for his survival. Does this mean that I can't get a Polish passport?

The documents I mentioned also mention my uncle and clearly state that his Polish by descent even though he was born in Italy. We have a copy of his birth certificate. My uncle's dob is THE SAME in all the documents including his current ID. I don't think my is aware of this because he doesn't have a Polish passport. Can I use this to prove that my grandfather is Polish? If so, would my uncle need to reobtain his Polish citizenship first?

If Poland refuses to accept these documents, can I get a Lithuanian passport since my grandparents were born in Vilnius (which is now part of Lithuania)? Also, if Poland refuses to accept these documents restore my uncle's Polish citizenship, wouldn't it mean that my uncle is Italian because he was born "stateless" in Italy?

My grandfather was born in Vilnius late 1915, back when it was occupied by the Germans. Does this mean that my grandfather was also a German citizen because he was born in what was "Germany" at the time? Can I use this to obtain German citizenship or PR based on https://en.wikipedia.org/wiki/German_na ... ersecution?

If you were able to get this far, thank you for reading all of this. Any information would be greatly appreciated.