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This familysearch wiki has a lot of information about both WWI and WWII enemy alien records, listing the records that exist and where they are.
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Dear Ms. Neumon,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located 147 series pertaining to enemy aliens in various record groups. Please review these series. For access to a particular series, please contact the National Archives location listed under the series contact information via email..
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request. We apologize for this inconvenience and appreciate your understanding and patience.
We also suggest that you review the NARA publication on the World War II Enemy Alien Control Program Overview.
We hope this is helpful. Best of luck with your family research!
There is a reply to a similar question here that may be useful.
The short version is that Registration Forms Filed by Resident Aliens in the United States, 1940 - ca. 1943 are at the National Archives in DC but access is restricted restricted by law.
Your best best is to try to find an A-File for them. See Alien Files (A-Files) at NARA.
If they were investigated, arrested, or detained, there might be more records. See the response to Seeking list of Italians detained in Louisiana. However, the vast majority of the Italians and Germans who registered as aliens were not arrested.