enquiring about "family trees" and citizenship by decent

Hi there
I was just wondering if anyone here knows where I can go or ask to find out about my ancestral line in Germany ..
My grandparents and great grandparents originally came from somewhere in Poland, moved to Germany during WW2 and landed up changing their names to German surnames. I'd like to find out how I would have to go about to find out where exactly they came from since they were registered in Germany before they died, and to see if it's possible to get citizenship by decent ..?

Thanks guys

You can only get German citizenship by descent (you don't need to be decent for this  :) ) if at least one of your parents was German citizen at the time of your birth.
Researching further back is therefore only required if the citizenship of your parents is in doubt. If you want to do that, you should contact and visit the family registries (and before WWII sometimes also church registries) of the places where your ancestors lived. There is no central place for keeping such documents, and all of them are available on paper only (meaning extended travel and detective work is needed to find them) - IF the records were not destroyed in the war or through some other misfortune.
There are companies offering this as a service, but it won't come cheap!

Duly noted, I'll look into it :) .
Thanks a lot for the info 😊👍🏾

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