...there is the Freedom of Information Act (justice.gov/oip/freedom-inform….)
And, last but not least, a lot of Americans are into #Genealogy. Locating any offspring of your US relatives might be enough as a starting point.

It seems like a fascinating story.

(I am aware that you probably know many of these possible leads, but as IDK which ones... ;)). //

The Freedom of Information Act, 5 U.S.C. § 552

^{www.justice.gov}